Black widows explained
The black widow spider (genus Latrodectus) begins by using its silk glands (spinnerets) at the rear of its abdomen to create a sticky web. It waits at the edge of the trap until its prey either ﬂies or walks into it. When an insect is trapped in the web, the black widow can sense the vibrations caused by the struggling prey. From these vibrations it can tell how big and strong the prey is, and if it is too big, it will leave well alone.
If the prey is small enough, however, the black widow will use its spinnerets to cover it in stronger webbing. It then ﬁrmly holds the prey with its chelicerae, which is a pair of hollow appendages above its mouth that send poison into the victim.
The spider’s latrotoxin, neurotoxic poison causes the prey to suffer spasms, paralysis and death within ten minutes. After this, enzymes inside the victim liquefy its body allowing the spider to feed on it.