Resin fossils mimic ants in spiders. Image source: George Poinar/History Biology
Some folks freak out at the sight of "Brown recluse," "Black widow," or even "Daddy longlegs" spiders due to arachnophobia, but predators of these arachnids don't share that fear. According to George Poinar, a paleontologist at Oregon State University, certain spider species have evolved deceptive defensive capabilities, disguising themselves as an unpopular prey—ants. Researchers published a paper in the latest issue of "Historical Biology," showcasing a spider mimicking ants preserved in resin fossils.
Many animals despise ants or perceive them as threats. Ants are defensively aggressive, armed with strong mandibles and venomous stings, capable of summoning scores of nestmates as allies. Yet, many spiders lack chemical defenses, often solitary, making them easy prey for larger spiders, wasps, and birds. However, these predators prefer to avoid ants. Thus, if a spider can mimic ants, it's less likely to be eaten.
The specimens used in the study were trapped in copal, a form of resin fossil. Copal, unlike amber, is an immature form of resin fossil, with a history possibly spanning up to 3 million years, whereas amber typically has a history of 25 million years or more.
The copal chunks originated from Medellin, Colombia, too "young" for age testing, which would otherwise damage the interior spiders. Poinar noted that there's no record currently indicating the presence of extant ant-mimicking spiders in settled Colombia.
The spider mimics of ants appear strikingly similar from the fossil specimens. However, for spiders, achieving this miraculous "disguise" poses a challenge: ants have six legs and two long antennae, while spiders have eight legs and lack antennae.
To bridge these anatomical differences, spiders typically position their first pair of legs in a manner resembling antennae. However, leg count and antennae aren't the sole features distinguishing ant-like appearances from spider appearances.
The abdomen and cephalothorax of spiders are closely joined, whereas in ants, these body parts are separated by a narrow structure called the petiole. Most scientists believe the transition began with spider mutations, adaptation, followed by natural selection.
However, Poinar suggests that this transition also involves some spider reasoning and intelligence, as spiders often mimic specific ant body changes in the same environment. Several groups of spiders have developed the ability to resemble various ant species, with some spiders attempting to disguise themselves as flies, beetles, and wasps, among other insects, to deceive their foes.
