The wolf, pirate and pelican spiders that prey upon their eight-legged peers
Going by the numbers, it may spiders seem to have a particular vendetta against insects. After all, eating up to 800 million tons of bugs every year takes some dedication, or at least some well-honed predatory adaptations. As it turns out, eating only bugs would leave a lot of other food on the table, such as spiders themselves, and so some species have diversified their diets. As great as spiders are at catching crickets and ants, it turns out that they’re great at hunting their fellow arachnids as well.
On the generalist side of things, wolf spiders will eat just about anything they can get a hold of— even small vertebrates. Instead of waiting in a web, spiders in the Lycosidae family travel along the ground or in burrows to hunt for prey while trying to avoid being eaten themselves. Some wolf spiders can be slightly strategic in how they hide and ambush their food, but for the most part they get by on speed and a bit of stealth.
Cellar spiders, often known as daddy long-legs, use more traditionally “spidery” tactics to catch their food. Their messy, tangled webs can catch a variety of insects, but they’ll also venture into other spiders’ webs to attack its original occupant. Their long, spindly legs help them move quickly over both their own and other spiders’ silk, giving them an edge when they feel like dining on arachnid.
Eriauchenius and Madagascarchaea spiders are a bit more specialized for picking off other spiders. Known more commonly as pelican spiders, these unusual predators have long “necks” and even longer chelicerae, the fang-tipped mouthparts that are much more modestly sized on other species. The combination of an elevated mouth and long chelicerae lets these spiders impale and hoist their prey off the ground like a hungry forklift, trapping prey in the air until they finally die. Specimens found in amber show that this lineage has been using this immobilizing strategy for at least 50 million years. They can be found in South Africa, Australia, and Madagascar, with the latter location being home to half the species alive today.
Pirate spiders in the family Mimetidae don’t have any special hook or peg-leg anatomy, as their names comes from the range of behaviors they use to acquire food. Rather than build their own webs, they search for other species’ webs to raid, usually starting with orb or cobweb weaver themselves. The pirate spider will first pluck at different threads in the web to imitate trapped prey in an attempt to lure the original spider into danger. Once in range, the pirate spider will lunge at its target, where a bite to the leg will immediately paralyze it’s meal thanks to the hunter’s spider-specific venom. Once the host spider is dispatched, the pirate may make use of the web to catch a few bugs as well, even eating other spiders’ eggs if it finds them.
This is by no means the complete list of spider-on-spider predation. For every specialized nest or venom, there’s probably another spider waiting for its next chance to eat some of its kin, assuming it doesn’t fill up on insects first.
Source: Who eats spiders? by Ben Goren, Spiderbytes