Science Interviews

Biting Insects

Ian Burgess from Insect Research and Development, Cambridge

Kat - Why do horseflies hurt so much when they bite you?

Ian - Normally, horseflies bite very large animals such as deer and cattle. These animals can't turn round and smack them one. Therefore they don't really have to creep up on you. They have very large mandibles and actually make a big hole in you! They then lap the blood up as it starts to flow out. With a thick skinned animal like a cow, they have to chew quite a big hole, but they don't adjust this when they're biting human skin. This means that it hits the nerves rather quicker.

Kat - Is it true that you can get bitten by spiders in the UK, because I'm sure I've been bitten at night by spiders.

Ian - there are several spiders that can bite in this country. There are a couple that live mostly in the south of England that are moderately venomous. Even the big house spiders can bite, particularly if you annoy them. In fact one of the house spiders we have in this country has been accidentally imported to the western seaboard of the USA, where it's spread further north every year. It's known as he hobo spider as it catches lifts on trains. Now it's reached Alaska, where it isn't nice to live outdoors, it lives in houses all the time. As it's quite venomous, there are lots of websites looking at the hobo spider and how it attacks people.

Chris - Do you know roughly how many of these spiders get shipped in each year?

Ian - Oh into this country, it's probably thousands but most of them don't survive. They come on chilled ships or aeroplanes, and it's too cold for them. But some of them do creep through. The ones that we get are mostly widow spiders.

Chris - They're lethal aren't they?

Ian - Only if you're under five or have a weak heart. Mostly they'll just make you feel really awful for about 24 to 48 hours.

Chris - What actually is it in the venom of a spider that actually makes those symptoms?

Ian - Widow spiders have what is known as a neurotoxic venom, which is one that attacks the central nervous system. It gives you shakes, tremors, vomiting and things like that. Some of the other spiders have what is called a cytolytic venom, and that causes tissue to break down, so you get a really nasty gangrenous reaction.

Kat - How aggressive are insects generally? We all know not to annoy a wasp because it'll come and sting you, but are there any really aggressive insects in the world?

Ian - Well I would probably say that bees are worse. Wasps are actually quite docile, except perhaps for the Asiatic hornet.

Bee - I think that William would know more about the Africanised killer bees, but domestic bees vary hugely. You can get all sorts of bees specially bred for different temperaments.

Chris - Is it true that when you blow smoke into a bee hive that it genuinely calms them down?

Ian - Oh yeah. Their response to a forest fire is to engorge on their honey so that they can then move out and save some of their food reserves. So if you blow the smoke in, they think it's a forest fire, they fill themselves up and get a bit dopey and drunk. So that's why they're less likely to be aggressive.

Chris - So that's a bit like us when we've had a massive Sunday lunch and just want to slump in the armchair.

Ian - Pretty much so, yes.

October 2005