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Ask An Entomologist @BugQuestions
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For tonight's #DeepDive, let's talk a little bit about how insects use venom *and* poison for various things.

The divisions can be weird, and there's a lot of ways that venoms and poisons can be used!

Thanks to @RosemaryMosco for comic permission!…
When we think of venom or poison, we typically think about the act of eating...and for good reason.

Venom/poisons are used to either help something eat, or keep something from being eaten.
The only exception to this that I'm aware of is the mating of the African rock scorpion.

During mating (2:10 in this video), the male stings the female.

This species doesn't use venom to hunt, so the exact reason behind this behavior is unknown.

The distinction between venom and poison isn't always so clear-cut. Venom can function as a poison under the right circumstances.

For example, sometimes ants will deliver formic acid straight into bite wounds. Sometimes, they just spray it everywhere.

For simplicity, we can divide eating into five stages:

1/2) Detection/Identification-finding the prey
3.) Approach-getting close to the prey
4.) Overpowering-subduing the prey
5.) Consumption-actually eating the prey

Venom or poison can be used at any of those last three stages
Poisons and venoms which are irritants, like in the ant example above, are usually intended to keep predators from getting close enough to eat.

Jellyfish can do something similar...releasing clouds of nematocysts into the water around them.
To overpower something, you don't necessarily need to kill it outright. You just need to make it unable to run away/fight.

Ampulex compressa appears to put it's prey into a very deep sleep to let it's larvae feed.

In insects, most venoms aren't designed to kill.

In fact, in parasitic wasps, the venom is used to subdue the prey by disrupting the host's immune system. In some species, there's no outward indication of the sting.
In social insects, however, venom is intended to kill. Aphids have a venom which causes the predator's immune system to kill the predator.

Poisons used to overpower prey are relatively rare, although they do exist.

One example would be the lethal farts that Berothids use to capture their prey.

H/T to @bug_gwen for this amazing article.…
A second example would be glow-worms, tiny flies which glow to attract prey to their webs.

They coat these webs in oxalic acid, which dissolves the exoskeleton just enough to cause their prey to die of dehydration.
The 5th stage of eating-consumption-is where a lot of poisons come into play.

Venom can be used to make an animal avoid something, and poison can be used to make it sick.

Most predators can learn to avoid 'bad' things.
Poison can be used in two ways to interfere with consumption.

First, some insects contain compounds which can irritate sensitive membranes. Paederus beetles, a tiny orange rove beetle, can destroy skin with it's chemical defenses.
On a less severe level, many poisons taste bad. For example, the quinones which make millipedes taste bad can also stain skin...even though they're not going to kill people outright.
The other main way that insects use poison is to fundamentally alter the physiology of potential predators.

This hornworm feeds on toxic plants, and stores the toxins it eats to defend itself.
Venoms and poisons are used in roles that revolve around eating...either to subdue prey with the intention of eating it or to subdue a predator to keep from being eaten.

It's also thought that venom is introduced through an injury (bite/sting) and poison is eaten or smeared.
Even though nature has a funny way of producing gradients, this definition produces a consistent and important series of differences we can use to tell the difference.
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