Saturday, 9 April 2011

A spider in ant disguise

ResearchBlogging.orgMy young daughter does not like ants. This is a bit troublesome at this time of the year when garden ants are everyhwere. Yesterday, she pointed at something on the ground. I looked at I saw what looked like an ant carrying another ant running very fast. It must have looked a bit odd as I stopped the "ant" putting my hand in front of it. She hid underneath and I slowly lifted my hand and took a couple of shots. Only when revising the shots did I realised that the ant was only an illusion: it was a spider, but one that strongly resembles an ant not only in size, general shape, shininess, but also in posture and behaviour. She carried her front legs raised so that it looks like its got antennae and six legs, and its movements were most reminiscent of the manic running of ants in hot weather.
In her review of ant mimicry in spiders Paula Cushing stated referring to morphological spider modifications to resemble ants:

They include a variety of color and body-form modifications that give the spider the appearance of having three body segments instead of two and of having long, narrow legs instead of shorter, more robust legs. Mandibles, compound eyes and even stings are sometimes mimicked by the spiders through modifications in the chelicerae, pigmentation in the cuticle, or special positioning of the spinnerets. In many cases, the extent to which the mimics resemble a particular model is extraordinary
The following table helps in dispelling the notion that this ant resemblance is just a fantasy of the observer.
There are many species of invertebrates that have evolved to resemble ants including crickets, bugs, beetles, springtails, and even flies. At least 100 species of spiders of 12 families mimic ants. The formal name for this phenomenon is ant mimicry or myrmecomorphy. But why would a spider evolve to look like an ant? A few spiders resembles ants in order to get close to them and eat them (aggressive mimicry), but most ant mimic spiders benefit because visual predators take them for ants, and avoid eating them. This is a case of protective or Batesian mimicry, the mimic imitating a dangerous model. Ants can be distasteful or aggressive or both, with biting jaws, a spray of formic acid and a sting. Given that the deception is visual the selective agent must be highly visual: birds, wasps, hunter spiders that normally avoid ants would avoid an ant mimic in the same way, therefore a small spider may have much to gain from resembling a common local ant. My little ant-spider is most likely Micaria pulicaria, a widespread species in the U.K. often found running in the company of common garden ants. It is not reported that it preys on ants so, the reason for its ant mimicry, most likely involves Batesian mimicry. Interestingly, it is the only diurnal genus in a mostly nocturnal hunter spider family - Gnaphosidae, for an example see this post - and ant mimicry might have help this spider lineage conquer and diversify in a diurnal niche.

Cushing, P. (1997). Myrmecomorphy and Myrmecophily in Spiders: A Review. The Florida Entomologist, 80 (2) DOI: 10.2307/3495552
Reiskind, J. (1977). Ant-Mimicry in Panamanian Clubionid and Salticid Spiders. (Araneae: Clubionidae, Salticidae) Biotropica, 9 (1) DOI: 10.2307/2387854


Tamara Kelly said...

Nice! I found something similar a few weeks ago - a spider trying very hard to look like an ant. Very small and brown. The giveaway was his body language didn't quite work otherwise I would have overlooked him. Gin Gin, Qld.

Anonymous said...

I found one of these, but it had a black body instead - the first thing I noticed was that it had eight legs.

Suzanne Conboy-Hill said...

Think I found one last night - in my bed! I evicted it to the kitchen but this morning it was dead. Not my doing, I don't think - it was wiggling its legs when I left it there. Brown, ant-sized and shaped but just a little too leggy. Like Tamara, I thought it didn't quite work as an ant but it was doing a good job of looking like one!

Anonymous said...

I found a spider mimicking an ant too, but it was a bit large for an ant though.... It's definitely a spider as you can see its eyes and 8 legs, but its body language comes across as an ant. I dont know what species it is, but I'd like to.