A mysterious butterfly

Credit: Chihuahuan Desert
Research Institute

About three years ago in spring 2011 the undergrad student Jon Spero found a dead butterfly beside a road next to our institute. The street cuts right through the campus of the University of Guelph and a large number of students need to cross it sometimes several times to get to their classes.

Admitted, finding a dead bug beside a road isn't something special worth a blog post but as it turns out this find is extremely unusual. Actually it was so unusual that it led to a paper that was published yesterday in the journal The Canadian Entomologist.

At first the find must have looked rather exotic and that spurred further interest. Thanks to the curiosity of Spero and his then supervisor, Alex Smith, the find was identified as lyside sulphur (Kricogonia lyside). The colleagues used DNA Barcoding to determine the species and its likely origin.

Kricogonia lyside adults winter in southern Texas, United States of America and typically disperse northward into the Great Plains in mid to late summer, but not in April. In the spring of 2011, lyside sulphurs were relatively scarce in southern Texas and were not reported further north until later in the year. Historically they have been recorded in summer as far north as Nebraska, Missouri, and Kentucky, and possibly Illinois, but never in Canada.

Kricogonia lyside is a small tropical butterfly colored pale yellow to white with few distinctive markings. It's caterpillars hide in bark crevices during the day, and come out to feed at night on their favorite plants of the Zygophyllaceae family (e.g. Guaiacum coulteri and Porliera angustifolia). Adults periodically make huge migrations - here a video of a mass emergence at the Rio Grande (or Rio Bravo) in Texas.

But the question is - how did this small butterfly got all the way up to Southern Ontario? The authors discuss several options in their paper and as you can see nothing was deemed impossible in the first place:

1. Natural dispersal of the butterfly from southern Texas to Ontario

2. Weather system transport of the adult butterfly

3. Transportation of butterfly specimen on or in a vehicle

4. Importation of a pupa on imported produce

5. Specimen dropped by an insect collector

6. April Fool’s Day joke

7. Escapee from a live butterfly exhibit

However, they provide compelling arguments to rule out all possible explanations for the find of the lyside sulphur although personally I wouldn't exclude number 2 just yet. Storms and strong climatic fronts often transport butterflies outside of their normal range and according to the authors a very strong weather system extending from southern Texas into eastern Canada was recorded around the time of the find.

In summary, it is highly likely that the lyside sulfur individual found in Ontario originated in southern Texas or northern Mexico[...]the way in which this unusual specimen reached Ontario remains a mystery.


h/t Alex Smith