How the ‘smell’ of an ant can save a parasitic butterfly

Friday 23 August 2013
The large blue butterfly

A species of rare British butterfly whose larvae feed on the blood of a certain type of ant is being saved from extinction thanks to a unique new test to identify the ‘smell’ of the prey species.

Stephen Martin, Professor in Social Entomology at the School of Environment & Life Sciences, University of Salford, is the lead researcher who is utilising a technique known as chemo-taxonomy to aid the conservation of a threatened species for the first time.

The large blue butterfly is hugely dependent on the prevalence of a particular species of ant, Myrmica sabuleti. The butterflies develop on grassland after females have laid their eggs on wild thyme, where caterpillars initially develop by feeding on the plant. The larvae eventually fall onto the ground where they are picked up by worker ants, who carry the larvae away to their nest. Once inside, the larvae feed off the ants’ blood before pupating within the nest.

This butterfly was declared extinct in Britain in 1979, but was successfully reintroduced from Sweden four years later after several attempts, although the success of reintroduction programmes remains haphazard. Therefore, populations remain small and fragmented across the country, whilst annual fluctuations in population sizes are considerable, leading to the risk of localised extinctions. The survival of the large blue butterfly in Britain is considered extremely important - it is listed as a priority species under the UK Biodiversity Action Plan and features within the EU Habitats Directive.

The butterfly’s initial decline in the UK was attributed to the loss of rabbit populations through myxomatosis and the subsequent displacement of the ants by Myrmica scabrinodis, a similar species which thrive in less grazed habitats. The survival rate of caterpillars is more than five times higher within the nests of the Myrmica sabuleti as opposed to any other species.

The successful reintroduction of the large blue butterfly entails correctly identifying the predominant species of ant within the ecosphere, something which can prove problematic and time consuming. Traditional methods involve morphological techniques, with experts taking painstaking measurements of the antennal lobe at the base of the ants’ antennae. In many cases, a whole range of measurements are needed in order to identify the ants correctly.

In contrast, the chemo-taxonomy method introduced by Professor Martin involves identifying organisms based on their unique surface chemistry. It is being recognised as a much faster, accurate and inexpensive means of separating species which are morphologically very similar. The technique involves measuring the presence or absence of two specific hydrocarbons (oils) found on the skin of the ant, which enables both the ants and researchers to easily identify one species from another, since these oils are used by the ants as species recognition cues.

Researchers confirmed that different ant species displayed consistently distinct hydrocarbon profiles, allowing for quick and easy identification.

The new chemo-taxonomy technique offers several advantages over morphological methods. Previously, large blue butterfly conservationists were required to be highly competent taxonomists. Now, identification through chemistry enables inexperienced and non-specialist ecologists to recognise one ant species from another. It also becomes possible for a large number of samples to be analysed quickly and accurately.

The research paper was developed in collaboration with PhD student Rhian Guillem at the University of Sheffield. 

Professor Martin said “With the use of chemo-taxonomy we are taking a significant step towards ensuring the success of large blue butterfly re-introduction programmes so that the butterfly can thrive across Britain once again.”

The research paper (Guillem et al., 2012) was published in one of the leading conservation journals 'Biological Conservation' and was developed in collaboration with PhD student Rhian Guillem at the University of Sheffield.

Using chemo-taxonomy of host ants to help conserve the large blue butterfly

Biological Conservation, Volume 148, Issue 1, April 2012, Pages 39-43
R.M. Guillem, F.P. Drijfhout, S.J. Martin