Insect bites & stings

Insects inhabit every corner of the globe and there are perhaps more species of insect than all the others put together. They are remarkably successful creatures and have adapted to survive in just about every environment.

Many species of insects are parasitic, living off a host rather than devouring it. Part of their success is this ability to prey off other species, including humans.

Biting insects such as mosquitoes and sandflies cause much inconvenience due to local reactions to the bites themselves which are rarely harmful, but in doing so they can spread diseases some of which are potentially fatal.

Insects will bite at any time of day but most bites occur in the evening so extra vigilance is necessary after sunset.

Other insects like bees, wasps and ants posses stings which can be quite painful and sometimes dangerous. Hundreds of stings by bees or wasps can be fatal due to direct toxicity.

Bites & stings

There are dozens of insects whose bites or stings cause problems, and they can be split into two categories: venomous and non-venomous. The tables below explain the main differences.

The difference between bites and stings

The difference is due to the nature of the bite or sting. Venomous insects attack as a defence mechanism, injecting painful, toxic venom through their stings. Non-venomous insects bite in order to feed on your blood. Although local irritation and allergic reactions to the saliva and anti-coagulants do occur from non-venomous bites, severe reactions such as anaphylactic shock only happen from venomous stings.

When bees sting, they leave the sting and venom sack attached. Venom continues to pump in through the stinger until the sack is empty or the sting is removed. The only good part about this is that bees die after they sting. Wasps and hornets however, don't leave their stings behind and can sting you over and over.

Venomous stings are always very painful, red, and swollen up to twelve inches around the sting site. This is called a local reaction. In sensitive individuals, a systemic or "whole body" reaction occurs, with redness, hives (itchy raised skin lumps), and swelling far away from the sting site. These systemic reactions can be life threatening and it is important to know the difference between them.

Those people with a known allergy to the stings should carry an emergency syringe with 0.1% adrenaline and know how to use it.

Biting insects themselves, aren't generally dangerous because allergic reactions are rare. They do however, spread diseases like Malaria, Yellow Fever, Lyme disease, Typhus, and Encephalitis, but for most of us their bites just cause terrible itching.

Protection against insect bites

The occurrence of mosquito and other insect bites can be minimized by wearing long-sleeved shirts, long pants, and hats to reduce exposed skin. Repellents applied to clothing, shoes, tents, mosquito nets, and other gear will enhance protection.

Bed nets provide protection and comfort when accommodations are not adequately screened or air-conditioned. Bed nets should be tucked under mattresses and can be sprayed with repellent. Aerosol insecticides and mosquito coils may help to clear rooms of mosquitos; however, some coils contain DDT and should be used with caution.

Tucking shirts into pants and pants into socks will increase protection. Boots also decrease the risk of bites. During outdoor activities and at the end of the day, travellers should inspect themselves and their clothing for ticks. Prompt removal of ticks may prevent infection.

Repellents containing DEET (N, N-diethylmeta-toluamide) are commonly available and effective against mosquitos, ticks, and other arthropods when applied to skin or clothing. Repellents with DEET concentrations of about 30% are quite effective and should last for about four hours. The possibility of adverse reactions to repellents can be decreased by taking the following precautions:

Apply repellents sparingly only to exposed skin or clothing
Avoid high concentrations of DEET
Do not inhale, ingest, or get into the eye
Never use on wounds or irritated skin
Wash repellent-treated skin after coming indoors
Pregnant and nursing women should minimise use
Avoid applying to children's hands that are likely to have contact with eyes or mouth

MozzyOff is a 100% natural midge and mosquito repellent and an alternative to DEET for those who cannot tolerate it.

Made from plant oils, MozzyOff offers you up to six hours protection from biting insects such as midges and mosquitoes, black fly and gnats. It's water resistant and unlike chemical based products, MozzyOff repellent will not harm synthetic materials. MozzyOff is also biodegradable and the packaging is recycled and recyclable so its good news for the environment too.

MozzyOff is kind to your skin and its inherent soothing properties mean that it will relieve the itch of previous bites and hopefully stop you getting bitten again.

Permethrin is also a highly effective repellent and insecticide for use on clothing, shoes, bed nets, and camping gear. Permethrin-treated clothing repels and kills ticks, mosquitos, and other arthropods and retains this effect after repeated laundering.

Protect yourself and your kids from mosquito bites as well as ticks and other harmful insects, with Permethrin Impegnated Insect Repellent Clothing. Click the graphic to browse the web site:

Treatment of bites

Itching is the main symptom to control with insect bites. Topical antihistamines and anaesthetics are for quick temporary relief; hydrocortisone cream has slower onset, but longer effect.

Ibuprofen Gel. For pain and swelling from insect stings, is an excellent anti-inflammatory with quick onset.
Hydrocortisone cream 1% This preparation improves both itching and swelling/redness. It actually has anti-inflammatory effects, not just symptomatic relief like the topical anaesthetics. However, it does take longer for full effect than topical anaesthetics.
Xylocaine Gel 2% For immediate relief from surface itching and pain.

Any systemic reaction should be seen by a doctor immediately. This includes hives wherever they may occur, swelling in the face, shortness of breath or wheezing, difficulty swallowing, and light-headedness or fainting. These usually occur within minutes to an hour after the sting.

Local reactions generally don't require professional care. However, if your local reaction causes enough swelling or pain to distract you from your normal activities or keep you awake despite basic treatment, you should see a doctor. If the redness/swelling is worsening after 24 hours, see your doctor.

Treatment of stings

First, the stinger must be removed. Pain, swelling, and itching are the main complaints. Home remedies include baking soda or meat tenderizer compresses to "draw out" or destroy protein-based venom. Scientific data is lacking with these techniques, but they do make logical sense. See the table below for medications which can help.

Sting removal

Place the edge of a dull table knife firmly against your skin next to the embedded stinger. Applying constant firm pressure, scrape the knife across your skin surface and the stinger. This removes the stinger without injecting more venom, which is what happens when you remove the stinger with tweezers or your fingers.

Mosquitoes

These are the familiar flying insects, (family Culicidae), numbering about 2,500 species, that are important in public health because of the bloodsucking habits of the females.

Mosquitoes are particularly dangerous insects since they are known to transmit such serious diseases as yellow fever, malaria, filariasis dengue and Japanese B encephalitis. They bite at any time of day but mostly in the evening.

Different species of mosquitoes show preferences and, in many cases, narrow restrictions as to host animals. They are apparently attracted to host animals by moisture, lactic acid, carbon dioxide, body heat, and movement.

The slender, elongated body of the adult is characterized by its long, fragile-looking legs and its mouth-parts, which are contained in an elongated proboscis. The threadlike antennae of the male are generally bushier than those of the female.

The males, and sometimes the females, feed on nectar and other plant juices, but in most species the females require a blood meal in order to mature their eggs, which are laid on the surface of water.

The eggs hatch into aquatic larvae, which feed on algae and organic debris; a few are predatory and may even feed on other mosquitoes. The adults mate soon after emerging from their pupal cases. The duration of the life cycle varies greatly depending on the species.

There are three important mosquito genera:

The genus Anopheles the only known carrier of malaria, also transmits filariasis and encephalitis. Anopheles mosquitoes are easily recognized in their resting position, in which the proboscis, head, and body are held on a straight line to each other but at an angle to the surface. The life cycle is from 18 days to several weeks.
The genus Culex is a carrier of viral encephalitis, west nile virus and, in tropical and subtropical climates, filariasis. It holds its body parallel to the resting surface and its proboscis is bent downward relative to the surface. The life cycle, usually 10 to 14 days, may be longer in cold weather.
The genus Aedes transmits yellow fever, dengue, and encephalitis. Like Culex, it holds its body parallel to the surface with the proboscis bent down. The wings are uniformly coloured. A.aegypti the carrier of yellow fever and dengue, has white bands on its legs and spots on its abdomen and thorax. Aedes usually breeds in floodwater, rain pools, or salt marshes, the eggs being capable of withstanding long periods of dryness. The life cycle may be as short as 10 days or as long as several months.

Some facts about mosquitoes

Why do mosquitoes bite? Only female mosquitoes bite. Female mosquitoes require a blood meal to acquire the protein needed to produce eggs. Females lay multiple batches of eggs during their lifespan, and a new blood meal is needed to produce each batch. Different mosquito species prefer different host species; some mosquitoes will seek blood meals from birds, others from mammals - and some are generalists. The female inserts her needle-like proboscis - a slender, tubular, feeding and sucking organ - under the victim's skin, drawing blood into her abdomen. She will feed until her abdomen is full, unless discovered and brushed away.

Why do mosquitoes seem to bite some people, but not others? This phenomenon is not completely understood. Mosquitoes are attracted by the carbon dioxide that we - and other animals - exhale. They may also be attracted by various odors - perfume, perspiration, lactic acid, detergents - that combine in unique ways to make one victim more attractive than another as a meal. Because dark colors absorb heat and lighter colors tend to reflect heat, mosquitoes also tend to be more attracted to victims dressed in darker clothes. Also, some people react more violently to the bites than others and only appear to be bitten more often.

Why do mosquitoes bites itch and swell? The itching, swelling, and burning from a mosquito bite are actually caused by the body's autoimmune response to the saliva injected by the mosquito when she feeds. This saliva contains anti-coagulating agents that prevent the victim's blood from clotting as it is sucked into the mosquito's abdomen. A bite may take several days to heal and stop itching; treat it with Calamine lotion or a topical anti-itch medication.

Where do mosquitoes breed? Mosquitoes breed in wet, swampy areas, where they lay their eggs. The eggs hatch in the water, and the young mosquitoes spend their pupal stages in the water. Mosquitoes lay eggs in both fresh and polluted water, and seek still waters such as those found in small puddles, ditches, and ponds. Even a small amount of standing water - say, in the bottom of a flower pot - will provide sufficient habitat for mosquito eggs. These eggs usually hatch about 5 days after they are laid. A key factor in mosquito prevention is the elimination of standing water in an area.

What is the average lifespan of a mosquito? Like most insects, mosquitoes are a prime food source for birds, amphibians, and spiders. Between predators and extreme weather events such as drought and harsh rains, most mosquitoes live for an average of about two weeks in their adult form. If they manage to escape predators, females from some mosquito species live to about two to three months of age. Those females who enter adult form late in the season may go into hibernation as cooler weather approaches, and can emerge the following spring to lay eggs. In many species, eggs laid before the onset of cold weather can also survive through a winter, even without water, re-hydrating in spring rains to go through larval, pupal, and adult stages.

How many types of mosquitoes are there? According to the American Mosquito Control Association, there are more than 2500 species of mosquitoes world-wide.

Sand flies

These include any insect of the family Phlebotomidae of the order Diptera. The aquatic larvae live in the inter-tidal zone of coastal beaches, in mud, or in wet organic debris. The adults are often called biting midges and are only 2 to 3 mm in length making them difficult to see.

Sand flies are found in almost any aquatic or semiaquatic habitat throughout the world. Many of the blood-sucking species are pests in beach or mountain habitats. They may also be vectors of disease-causing viruses, protozoa, and filarial worms. The bite is not painful but often causes an allergic response which becomes very itchy. Some people get a red weal 1-2 inches wide! Avoid scratching the weals; it makes them itch longer and can lead to infection.

Sand flies are of considerable medical importance: around the Mediterranean and in southern Asia, Phlebotomus transmits the pappataci fever virus; and in parts of South America, Africa, and Asia it carries the protozoan parasites causing kala azar, Oriental sore, espundia, and bartonellosis.

The name sand fly is also used for certain species of the black fly and the biting midge. They are often referred to as No-See-Ums because you rarely see them.

More than just an irritation

Lurking on the beaches of many of our favourite holiday and diving resorts is a disease that can do more than just ruin your holiday.

It's a disease that can haunt you for months after you return home, and even ruin your life. Though it's not as widely known as malaria, it can be every bit as painful, tenacious, and dangerous.

Worse yet, the source of the infection is nearly invisible - the ubiquitous no-see-um - the disease it transmits - Leishmaniasis.

If you've never heard of leishmaniasis, you're hardly alone. The culprits that spread the disease, commonly referred to as no-see-ums (because you hardly ever see them), are minute insects of the genus Phlebotomus often called "sand flies" and like mosquitoes, the gestating female no-see-ums hungry for protein go in search of a "blood meal". It is during the process of feeding that they transmit the protozoan parasites responsible for the disease.

It is also possible for a fever and rash to develop after receiving several no-see-um bites as a reaction to the toxins in the bites themselves, and multiple no-see-um bites can cause death from their toxins alone.

Leishmaniasis currently affects around 12 million people in 88 countries (with 2.5 million new infections annually).

It is considered a dynamic disease whose range is constantly spreading which is now well entrenched in the Mediterranean, North Africa, The Middle East, South East Asia, Central America and the Caribbean.

In its cutaneous form, leishmaniasis is characterized by a skin sore or sores that develop weeks or months after transmission. Sores typically leave scars, and some forms can be severely disfiguring.

Visceral leishmaniasis, traditionally known as kala-azar may take months and even years to develop and is fatal if untreated. Symptoms include fever, weight loss, cough, diarrhoea, lethargy, enlargement of the spleen and liver, and anaemia. Both forms require a biopsy for diagnosis.

Though leishmaniasis only accounts for a small percentage of tropical infections, unless the victims consult physicians specializing in tropical medicine, diagnosis is often inaccurate. The disease is quite difficult to cure and victims are prone to recurrences.

For decades the most effective treatment has been considered to be sodium stibogluconate, but the three-week intravenous regimen is relatively toxic, and the parasite is reportedly becoming antimony-resistant in some areas so there is no guarantee that it will not recur. Other treatments are available, but no cure is 100% effective, and there are currently no vaccines available.

With no certain cure, prevention is definitely the key. No-see-ums are usually more of a problem at night and when the wind dies down on the beach. The first line of defence is to cover yourself with insect repellents containing DEET. Wear long-sleeved shirts, long trousers, and socks in the evenings.

While the odds of bringing home leishmaniasis are probably too small to allow it to influence travel plans, the consequences of infection are so unpleasant that it makes good sense to take aggressive steps to avoid becoming the main course for a hoard of hungry no-see-ums.

If on return from an endemic area, you develop persistent sores that you fear may be indicative of leishmaniasis, ask for a referral to a tropical medicine specialist.

Tsetse flies

Tsetse flies can be anything from 7 to 15mm long. They are sturdy flies not unlike houseflies and they have a painful bite. They spread the disease known as sleeping sickness (Trypanosomiasis) which is caused by a single celled motile organism. The disease is serious and sometimes fatal and is difficult to treat. There is no vaccine available. Sleeping sickness is thought to be present in 36 countries of sub-Saharan Africa.

Tsetse flies require shade and humidity and tend to occur along rivers and lake shores in association with game animals. They are attracted to the scent of animals, movement and bright colours.

Fleas

Adult fleas are about 2mm long, wingless, and have three pairs of legs. The hind pair of legs is modified for jumping. Fleas are reddish-brown in colour and vertically flat like a fish, and can move easily through the hair of a host. They feed on the blood of their hosts.

Fleas breed wherever their host sleeps. Flea eggs are small and white. The larvae of the flea look like small white worms with dark heads. They live on the floor and feed on organic debris. They form pupae which can lie dormant until they sense a suitable host passing by and then they come out to feed.

The human flea, (Pulex Irritans), is almost extinct in Europe but other types of animal flea are much more common and will bite humans especially when they cannot find their usual animal host or if they become very numerous. Their bite often leaves a small, red, irritated area.

Flea bites tend to occur in groups, along clothing constrictions and around the ankles. They often pass out undigested blood leaving tell tale blood spots on bed sheets.

Some types of flea, especially rodent fleas, are able to transmit diseases. Two of the more well known are endemic typhus and plague. However these diseases are quite rare and confined to the poorest areas of urban squalor.

Chigoe fleas

These fleas are endemic to Central America and West Africa. They live outdoors in dry sandy locations. The female penetrates the skin around the toes and then swells up with eggs causing inflammation and ulceration. Gangrene can set in if left untreated. Avoid going barefoot in areas known to be infested.

Lice

There are three types of louse that affect humans; the head louse, the crab louse and the body (clothing) louse. The head louse lives on the scalp, the crab louse lives in pubic hair and sometimes arm pits and beards, and the body louse infests clothing. They all feed by sucking the blood of their host and they are spread by intimate contact or by sharing clothes.

The best evidence of louse infection is the discovery of the tiny egg cases called nits attached to body hair or clothing.

The only significant disease spread by lice is typhus which is spread by body lice and is restricted to the very poorest areas. Otherwise lice are merely a nuisance because of allergic reactions and minor skin infections caused by their bites.

Ticks & mites

Travellers walking through dense undergrowth or exploring caves may find ticks or mites attached to their skin but they are relatively easy to remove with a pair of tweezers: grip the tick firmly under the head end and push down to disengage the "teeth" then gently pull away. Once the tick has been removed, treat the bite area with antiseptic.

Ticks are responsible for spreading diseases such as typhus, encephalitis and lyme disease.

Scabies is caused by a small mite which burrows into the outer layers of the skin and cause the characteristic itch which can be almost unbearable but the mite does not carry any infectious disease.

Scabies is caused by a small mite which burrows into the outer layers of the skin and cause the characteristic itch which can be almost unbearable but the mite does not carry any infectious disease. In order to catch scabies it is necessary to be in close contact with an infected person for some time. The itch develops six to eight weeks after infection. Treatment consists of applying an insecticidal lotion containing benzyl benzoate, malathion or carbaryl.

One species of mite endemic to South East Asia can cause Relapsing Fever which is a form of typhus.

Note: Ticks and mites are actually arachnids and not insects.

Bugs

Bed bugs are oval shaped and flat, reddish-brown in colour and can grow up to 10mm in length. They live in bed frames, cracks in the wall, under wallpaper etc. and come out after dark to feed when their victims are asleep.

They do not carry any diseases but their bites can be very uncomfortable. They tend to bite the face, arms and legs where they protrude from the bedclothes.

In South and Central America cone-nosed (assassin) bugs are common in rural areas where housing standards are low. They can grow up to 4cm in length with a thin head and long mouth parts. They can transmit Chagas Disease (South American Trypanosomiasis) which is a serious and sometimes fatal illness. Like bed bugs they live in cracks in walls and come out at night to feed.

If you are staying where either of these bugs are suspected, move your bed well away from the wall and if possible leave a light on in the room all night because they prefer to feed in the dark.

Chiggers

Chiggers are the parasitic larvae of the harvest mite, Trombicula alfreddugesi. The adults are harmless, but the tiny, six-legged larval stage is parasitic on many animals, including rodents, birds, rabbits, livestock, reptiles, toads, and humans. The biting season is therefore limited to the late summer/early autumn period when the larvae are active.

Chiggers occur in several parts of the world including the southern United States and do not normally transmit disease. However, in parts of Asia they are known to carry "scrub typhus".

They are normally found in brush and tall grassy areas, especially where small rodents are abundant. Females lay eggs on the ground in groups of up to 400, picking damp but well drained sites. They may be particularly abundant near river banks and under trees or bushes.

The larval chigger is an active creature that moves to the tip of grasses and fallen leaves to wait for and grab onto a passing host. Once on its host, the chigger usually moves about until it reaches a place where it is somewhat protected, such as around ankles, under socks, waistline, under belts and elastic bands of underwear etc.

Chiggers do not burrow into the skin, but they do pierce the skin, (often around a hair follicle) and after secreting digestive enzymes in their saliva, they suck up the liquefied host tissues. The rash and intense itching associated with chigger bites is an allergic reaction to their salivary secretions.

After a larva is fully fed days, it drops off the host, leaving a red welt with a white, hard central area on the skin that itches severely and may later develop into dermatitis. Welts, swelling, itching, or fever will usually develop three to six hours after exposure and may last for weeks depending upon the sensitivity of the individual. Scratching a bite may break the skin, resulting in secondary infections.

Insect repellents containing DEET (diethyltoluamide) are effective in repelling chiggers. For maximum effectiveness, repellents should be applied to shoes, socks, pant cuffs, ankles and legs, and around the waist. They move around the body for several hours before feeding so bathing soon after exposure to chigger-infested areas may wash the chiggers off your body and prevent feeding. Take a good hot bath or shower and soap repeatedly.

Applying benzocaine cream, hydrocortisone cream or calamine lotion may give temporary relief from the itching.

Prevention of bites & stings

There are basically two types of prevention of insect bites and stings:

Repellents and avoidance

Insect repellents work well for biting, non-venomous insects, but not against angry stinging insects.

Despite advertising claims, no oral products have ever been shown to be effective insect repellents.

Avoidance techniques for bites and stings are summarized in the tables below:

Avoiding stinging insects

Don't wear perfume or scented lotions.
Control odours at picnics, garbage areas, etc.
Avoid brightly coloured clothing outdoors.
Destroy or relocate all known hives or nests near your home.

Avoiding mosquitoes, chiggers, and ticks

Cover as much of your skin as possible with clothing, hats, socks, etc.
Pay special attention to cuff areas at ankles, wrists, and neck.
Avoid swamps (mosquitoes), dense woods, fields, and brush (ticks, chiggers).
Examine exposed skin and scalp areas for clinging ticks after returning from hikes.
Use insect repellent.