If you’re like me (and I know many of you are), you spend a fair amount of time poking about in ant nests. Nests usually contain developing larvae, of course, which some species maintain in an ungainly pile. In others, young are spaced along the walls and roof of the chambers. Like so:

Pheidole floridana larvae adhered to the roof of their brood chamber. Note how the larvae are all oriented with their backs to the substrate. These were stuck to the underside of a rock that I flipped, exposing the nest. (Austin, Texas).

How do ants hang their larvae? Thanks to a simple experiment published today by Clint Penick in PLOS ONE, now we know: larvae of a particular age have little anchors.

Schematic (A) and scanning electron micrograph (B) showing the anchor-shaped hairs on a larva of the harvester ant Pheidole rhea. Modified from Figure 1 of Penick et al 2012.

Not all larvae of all species have these hooked hairs. Rather, the structures appear in older instars of several disparate myrmicine genera like Pheidole, Cephalotes, Crematogaster, Strumigenys and Temnothorax, among others. I had a look through my old photos. Sure enough, for the indicated taxa, many larvae appeared hairy and/or stuck to something.

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The larva at left in this image of a Crematogaster emeryana brood nest shows the anchor hairs.

To confirm the  function of the anchor hairs, Penick et al performed an obvious test of the velcro hypothesis: They gave the grubs a haircut.

If the larvae still adhered to the test walls, some other mechanism must be at work. If the larvae fell, the hypothesis is supported. How well did shorn larvae stick?

Larvae with their anchor hairs cut dropped like rocks compared to anchored controls. Modified from Figure 3 of Penick et al 2012.

Poorly, if the walls were vertical, and hardly at all at greater angles. An elegant result! It appears the hairs-as-anchors hypothesis is correct.

And as far as I know, this may be the first time ant babies have been given haircuts for science.


source: Penick CA, Copple RN, Mendez RA, Smith AA (2012) The Role of Anchor-Tipped Larval Hairs in the Organization of Ant Colonies. PLoS ONE 7(7): e41595. doi:10.1371/journal.pone.0041595