Here’s a spider whose barf is worse than its bite

First, swaddle a fruit fly or other tasty prey in silk. Then barf toxins all over it. That’s how one type of spider prepares to dine.

Giulia Zancolli recalls the moment she read this detail. She had been reviewing another lab’s scientific paper. That paper was being considered for publication in a science journal. She was puzzled by idea of a spider vomiting lethal toxins on its prey. “What are you talking about?” she remembers wondering.

Looking for more info, she found a drawing from a 1931 scientific paper. At the time, she recalls, “that was the only evidence we had” that this account was for real.

Yet that silk-wrap-and-toxic-barf routine turns out to be exactly how the feather-legged lace weaver (Uloborus plumipes) kills its meals. Zancolli and her team described this novel approach to food prep June 13 in BMC Biology.

To confirm the behavior, these researchers needed to find living spiders to study. So Zancolli and her co-workers scoured plant shops and landscaping nurseries. Those are easy places to find lace weavers.

Watch as this feather-legged spider wraps its prey.

“You would probably not even notice them,” she says. With “very delicate” bodies, they often fold their front pair of legs forward. In this position, she notes, they could easily be mistaken for “a piece of dry leaf.”

They will encase their prey in silk, sometimes wrapping a hundreds-of-meters-long strand around and around and around it.

Most spiders subdue their dinner by injecting it with venom from fangs. But cross sections of the heads of feather-legged lace weavers revealed rounded blobs of muscles where venom glands should be.

The lace weavers do have fangs — but they lack ducts needed to inject anything. Instead, the researchers found a different clue in the spiders’ gut tissue. There, they found signs of genes that lead to producing ample, potent toxins.

Biologists reserve the term venom for an injected poison. The upchucked toxins, particularly from the spider’s midgut, proved as deadly as the venom of common house spiders. In tests, injecting the barfed-up toxins into fruit flies killed them.

And come meal time, the small predators take no chances when it comes to dosing. They don’t just drool a bit on their silk-prepped entree, Zancolli says. They instead liberally slather it all over their restrained meal.