Veromessor pergandei worker ants respond to the chemical alarm signal of a sister ensnared in silk

Worker ants come to the aid of a nest mate (centre) trapped in a spider web. Credit: C. L. Kwapich

Animal behaviour

Rescue ants save the day for comrades entangled in spider silk

Every life matters to one species of desert ant, despite its colonies numbering in the tens of thousands.

A desert-dwelling ant laboriously demolishes spider webs to rescue trapped nest mates — a risky mission few prey species would tackle.

Veromessor pergandei harvester ants, which thrive in colonies tens of thousands strong in the southwestern United States, usually walk a single route each day to collect seeds. Christina Kwapich and Bert Hölldobler at Arizona State University in Tempe monitored the ants’ response when one of their own became ensnared in a spider web.

If the entangled ant released a chemical alarm signal, its companions rescued it, carried it back to the nest and cleaned the silk from its body. Ants also tugged on the web itself until they had destroyed it. In laboratory tests, ants needed between 30 minutes and 2 hours to demolish a single web.

The authors say that although one ant represents only a fraction of the colony, rescue attempts might promote the colony’s long-term survival. This is probably in part because the loss of multiple foragers to webs every day could drastically reduce the number of seeds harvested per year.