African Pest Cricket Squirts Blood
Offensive Chemicals Deter Predators but Encourage Cannibalism
Some insects bleed a lot when attacked, but one species of cricket actually projects its blood towards predators. This deters them, but unfortunately it seems to attract other crickets who take over where the predator left off!
Ground Crickets as Pests
Many species of cricket cause damage by eating crop plants, and the Armoured Ground Cricket (Acanthoplus discoidalis) can destroy up to 30% of the millet crop in Namibia.
Ground Crickets Squirt Blood to Deter Predators
The Armoured Ground Cricket (Acanthoplus discoidalis) is tough and covered with sharp spines (as the name might suggest), but it also squirts blood and vomits when attacked. The blood smells (and probably tastes) nasty, and it seems to be an effective way of escaping predators such as lizards.
Ground Crickets Squirt Blood and Encourage Cannibalism
While vomiting and squirting noxious chemicals might help avoid predation from other species, the tactic backfires somewhat by attracting other crickets who then become cannibals. Individuals that avoid becoming lizard food therefore risk being eaten by their relatives!
When swarms of field crickets congregate the risk from cannibalism is so great that any injured animals are rapidly devoured, and this can be seen where animals are squashed on the road. As more and more crickets arrive to feed on their dead companions they too are likely to be run over, and large ‘pancakes’ of cricket remains can accumulate.
Presumably population density determines the effectiveness of this escape tactic in this species. Widely-spaced individuals find it useful, while those in a swarm do not.
Other Animals that Squirt Blood
Some katydids and a few beetles will also squirt blood when handled, and although no research has yet clarified the effects it is likely that the behaviour is defensive. In all cases the blood smells nasty to humans, and is presumably offensive to other animals as well.
Interestingly some species of Horned Lizard (that feed on insects with noxious blood) also squirt their blood at predators. When attacked, or handled roughly, they can project an accurate stream of blood from a space behind their eyes for several feet (watch video). The effect that this has on would-be predators is obvious to the casual observer.
Similarly, in the case of insects that bleed a lot when attacked, ‘common sense’ might well suggest that the behaviour is defensive, but it was not until April 2009 that this was convincingly shown to be true (‘There will be blood: autohaemorrhage behaviour as part of the defence repertoire of an insect’, Philip Bateman, Journal of Zoology 278).
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