Piotr Naskrecki was taking a nighttime walk in a rainforest in Guyana, when he heard rustling as if something were creeping underfoot.
When he turned on his flashlight, he expected to see a small mammal, such as a possum or a rat.
“When I turned on the light, I couldn’t quite understand what I was seeing,” said Naskrecki, an entomologist and photographer at Harvard University’s Museum of Comparative Zoology.
A moment later, he realized he was looking not at a brown, furry mammal, but an enormous, puppy-size spider.
Known as the South American Goliath birdeater (Theraphosa blondi), the colossal arachnid is the world’s largest spider, according to Guinness World Records.
Its leg span can reach up to a foot (30 centimeters), or about the size of “a child’s forearm,” with a body the size of “a large fist,” Naskrecki told Live Science.
And the spider can weigh more than 6 oz. (170 grams) — about as much as a young puppy, the scientist wrote on his blog. [See Photos of the Goliath Birdeater Spider]
Some sources say the giant huntsman spider, which has a larger leg span, is bigger than the birdeater.
But the huntsman is much more delicate than the hefty birdeater — comparing the two would be “like comparing a giraffe to an elephant,” Naskrecki said.
The birdeater’s enormous size is evident from the sounds it makes. “Its feet have hardened tips and claws that produce a very distinct, clicking sound, not unlike that of a horse’s hooves hitting the ground,” he wrote, but “not as loud.”
In the meadows of Europe, colonies of industrious team-workers are being manipulated by a master slacker.
The layabout in question is the Alcon blue butterfly (Maculinea alcon) a large and beautiful summer visitor. Its victims are two species of red ants, Myrmica rubra and Myrmica ruginodis.
The Alcon blue is a ‘brood parasite’ – the insect world’s equivalent of the cuckoo. David Nash and European colleagues found that its caterpillars are coated in chemicals that smell very similar to those used by the two species it uses as hosts.
To ants, these chemicals are badges of identity and the caterpillars smell so familiar that the ants adopt them and raise them as their own. The more exacting the caterpillar’s chemicals, the higher its chances of being adopted.
The alien larvae are bad news for the colony, for the ants fawn over them at the expense of their own young, which risk starvation. If a small nest takes in even a few caterpillars, it has more than a 50% chance of having no brood of its own.
That puts pressure on the ants to fight back and Nash realised that the two species provide a marvellous case study for studying evolutionary arms races.
Theory predicts that if the parasites are common enough, they should be caught in an ongoing battle with their host, evolving to become more sophisticated mimics, while the ants evolve to become more discriminating carers.
These insects make a particularly good model for such arms races because their geographical ranges overlap in a fractured mosaic.
Alcon blues lay their eggs on the rare marsh gentian plant and it’s there that they first grow before being adopted by a foraging ant. Both gentians and butterflies are rare but the ants are common, meaning that only a small proportion of colonies are ever parasitized.
The result is a series of evolutionary hotspots where the two species wage adaptive war against each other in contrast to the many coldspots where colonies never encounter the deceptive butterflies.