Bat Hibernacula and Herald Moths

Herald moth in a cave. Photo by Graeme Wilson, 2024.

This article is adapted from a post on David’s Bat Blog.

When carrying out hibernacula surveys, we often come across other species. Mosquitoes and bees are occasional discoveries, but the ever-present companion of hibernating bats is the Herald Moth (Scoliopteryx libatrix), sometimes there are one or two, but occasionally many dozens in one location.

Herald moths are pretty animals, with wavy-edged wings perfectly camouflaged with reds and browns so they can disappear into leaf litter and avoid predators. As a member of the Noctuidae family of night-flying moths, they have developed a rudimentary hearing organ. They use this to listen out for the echolocation calls of approaching bats. When they hear a bat, they take up an erratic flight path so the bat is unable to catch them.

Herald moth with condensation. Photo by Corrine Sim, 2024.

As with all things in nature, this new adaptation has not gone unnoticed. Long-eared bats (Plecotus spp.) have evolved particularly sensitive hearing to ‘out-hear’ their prey. Combined with their slow flying speed, they can get by with very faint echolocation calls for navigation, and it’s a strategy that works incredibly well. One of the common signs of a brown long-eared bat is a pile of discarded moth wings.

According to Butterfly Conservation, there are over 2,500 species of moth in the UK. Herald moths appear to be the only species choosing to overwinter in caves and mines, and we have little explanation for this unique strategy. It’s quite common to see hibernating bats with droplets of condensation in their fur, and we frequently see Herald moths with condensation on their wings and even on their antennae.

A brown long-eared bat with one ear fully extended and the other partially extended. These ears help them catch moths without alerting them to their presence with loud echolocation calls.

Preserving hibernation sites for bats helps to maintain essential ecological features for a range of species, and our work at Upper Middleton Quarry was included in the 2023 Bat Mitigation Guidelines as an example of good practice.


For more information on Butterfly Conservation go to http://www.butterfly-conservation.org

Another good source of information on moths: http://ukmoths.org.uk