Sunday, December 5, 2010

Blood Suckers and Poison Injectors

There are millions of insect species in the world. A few of them affect us by biting us and sucking our blood. In New Zealand we have fewer such insects than many other parts of the world, but there are several that are more than just a nuisance; they negatively affect our health.

Mosquito
Mosquitoes, fleas and bed bugs use needle like mouthparts to penetrate the skin and suck our blood. Proteins in the anaesthetic and anti-coagulants that they inject before extracting blood can cause itchy immune reactions where bitten. In many parts of the world, but not normally in New Zealand, mosquitoes and fleas transmit disease to humans. Mosquitoes can transmit malaria and dengue fever and fleas can carry murine typhus and salmonella. Bed bugs are on the increase worldwide but have never been shown to be implicated in disease transmission. However, the bites of bed bugs, as with mozzies and fleas can become infected, particularly when scratched.

Other biting insects include New Zealand’s sandfly or black fly. The female sandfly doesn’t bother with anaesthetic she just takes a bite at the skin and then sucks up the resulting drop of blood. She hopes to be able to fly away before she can be swatted. Horse flies and their like have similar feeding habits to sandflies, but their larger size can make their bites even more painful.
The Kiwicare website and help desks are contacted often for advice on identification of what insect or spider might be causing ‘bite marks.’ It can be very difficult to identify the insect or spider that has caused a bite just from looking at the bite. Bites tend to form similar sorts of localised reddening and swelling because the marks are caused by our immune systems reacting to foreign substances; whether proteins in the anti-coagulants and anaesthetics or just the physical damage caused by the bite. There are however some indications that can help to identify what pests might be responsible:
  • Bed bugs often give several bites in a straight line.
  • Fleas tend to feed at ankles, lower legs, wrists and torso.
  • Spider bites involving venom usually cause pain prior to inflammation.
  • If there appear to be two puncture wounds at a bite site this may indicate a spider is the culprit; spiders use two fangs to bite and inject their venom.
With insect or spider bites a puncture wound is usually visible and often includes the release of a small amount of blood. If no puncture wound is found it is possible that a red mark and swelling is due to some other skin reaction or damage to the skin caused by some other physical injury.

Just talking about fleas or bed bugs commonly makes people feel itchy and scratch the skin in response. Scratching can cause reddening and inflammation that can be mistaken for bites. It is therefore not easy for medics or pest experts to identify red marks as bites never mind being able to identify the possible culprit. However, if bed bugs, fleas, white-tail spiders or other biting insects are found then appropriate treatment to eradicate the pests can reduce the risk of bites.

A mosquito, a flea and a bed bug walk into a bar and order blood orange juice.
They get chatting and bragging about their capacity to suck blood. They decide to have a competition to see who can suck the most blood. They've got half an hour before meeting back at the bar.
When they return the bed-bug has blood dripping from his proboscis. "Where did you get that?" ask the mozzie and flea.
"From a woman asleep across the road" says the bed-bug.
The flea has blood all over its feet and is bloated, red and full of blood. "Where did you get all that?"asks the bed-bug and mozzie.
"From a tramp down in the park." Says the flea.
The mosquito's head is covered in blood. It's still dripping. "Where did you get all that blood?" ask the flea and the bed bug, most impressed.
"Do you see that bedroom window over there?" Asks the mozzie. "Yes" Say the bed-bug and flea"
"I didn't!" says the mozzie. Dazed.

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