Subject: Yellowjackets vs. butterflies, Alaska

From: Kenelm Philip <[email-masked]>
Date: Tue, 8 Aug 1995 22:18:46 -0800

Earlier this summer I reported on the strange absence of butterflies
in the Fairbanks area following the record crop of yellowjackets (_Vespula_)
last summer.
        Now that the collecting season here is essentially over, I can sum-
marize what happened to the butterflies:

        In the Fairbanks area, most species of butterflies were (as regards
adults) down to less than 1% of normal levels, with the following exceptions:

1) Adult hibernators (_Nymphalis antiopa_, _Polygonia faunus_, _P. gracilis_)
were present at near-normal numbers.

2) Odd-year species, which produce adults in odd-numbered years only (_Hes-
peria manitoba_, _Oeneis jutta_, _Erebia disa_) in taiga habitats, were
doing fine.

3) Tundra species (as: _Colias canadensis_, Clossiana polaris_, _Oeneis
melissa_, _Erebia fasciata_) were unaffected, and were out in good numbers
on Fairbanks-area hilltops like Murphy Dome and Wickersham Dome.

4) One small pocket was found near the Tanana River at the base of a steep
slope with steppe habitat, where several taiga species flew in good numbers.

        In Delta Junction, 100 miles ESE of Fairbanks, _Erebia epipsodea_
had a population explosion, and other butterflies were obviously not af-
fected by the yellowjackets. Delta did not have the yellowjacket outbreak
that Fairbanks did in 1994.
        From Delta to Tok (200 miles ESE of Fairbanks) the Tiger Swallowtail
(_Pterourus glaucus_)--which was very scarce in Fairbanks--was out in huge
numbers along the Richardson Highway. The road was covered with road-killed
butterflies. I would guess that traffic took out far more Tiger Swallowtails
between Delta and Tok each day than the Alaska Lepidoptera Survey has taken
all over Alaska and the Yukon in its 25 years of existence...
        At Tok, butterflies of several species were very numerous along the
roadside (including _Oeneis chryxus_). Tok also had no problem with yellow-
jackets in 1994.
        Along the Nabesna Road (south of Tok, and south of the Alaska Range)
_P. glaucus_ was also abundant. _Colias krauthii kluanensis_ and _Speyeria
mormonia_ were very abundant (more so than in 1994) at the end of the
Nabesna Road. According to the Wrangell-St. Elias National Park staff, there
was no outbreak of yellowjackets in that area either.

        The evidence supports the idea that predation by yellowjackets on
butterfly larvae was responsible for the crash in butterfly numbers this
summer. The yellowjackets do not fly in tundra, so were not a factor on
the hilltops. It is not known why the odd-year species were protected--
they were presumably in late-instar larval stages in 1994. The adult hiber-
nators were protected by being out of the larval stage during the period,
in late summer, when yellowjacket numbers peaked.

        It will be interesting to see how long it takes the butterfly
populations to recover. In 1992, when a freak period of cold weather and
snow in late spring knocked most butterflies in Interior Alaska and the
southwestern Yukon down to around 10% of normal levels, the recovery to
normal levels occurred the following summer.

                                                   Ken Philip
[email-masked]