Pennsylvania Crane Flies: Taking Stock (Nov/Dec 1996)

by Chen W. Young
Until recently, large natural history museums concentrated mainly on basic research
on the evolution and classification of organisms, and were only indirectly involved
with living systems. Today, we have entered a new frontier that has direct and immediate
benefits to environmental issues of increasing public importance. By mobilizing their
data-rich collections and collaborating with conservation organizations, government
agencies and private citizens, museums are working to satisfy expanding demands for
biological information that contribute to effective stewardship of natural habitats.
An example of this environmentally useful research is the current survey of the
crane flies of Pennsylvania, a three-year collaborative effort between Carnegie Museum
of Natural History and the Academy of Natural Sciences in Philadelphia. The goal is
to establish a comprehensive database of Pennsylvania crane fly sitings.
What most people think are large mosquitoes are actually crane flies. The adult
crane fly, or Tipulidae, is part of a large family of 5mm- to 50mm harmless flies
with elongated bodies, narrow wings and slender legs. The immature stages, or larvae,
can be found in many different habitats that provide food in the form of dead leaves
and other organic material. Locations include fast-flowing streams, algae and mosses
on rock faces, decaying vegetable material along streams and ponds, rotting leaves
and wood on the forest floor, and soil in lawns and pastures. Adult crane flies are
often abundant in moist woodlands or along streams near habitats where the larvae
develop. Within ecological systems they are a significant food supply for birds, frogs,
spiders and other insects. In North America, more than 1,500 species of crane flies
have been described. Without any specific sampling program, we know of more than 350
species in the state of Pennsylvania.
Our inventory of these insects is proceeding through several stages, typical of
biotic assessments of this kind at Carnegie Museum of Natural History. First we construct
a database of species and locality records culled from scientific literature, our
own collection of specimens, and specimens from other museums. Then we begin fieldwork,
sampling crane flies across the state and concentrating on critical, unique and special
habitats, paying particular attention to species considered to be rare, threatened
or of special concern. The last step is distributing the database to interested individuals
and agencies. In the future we will summarize these data for a wider audience by producing
a crane fly identification guide with information on habitat, distribution and natural
history.
Such an inventory is a necessary first step for using this diverse group of flies
as an indicator of ecosystem health. The presence or absence of indicator species,
including common ones as well as rare, are tell-tale signs of ecological function
in Pennsylvania habitats. Inventories establish the baseline data on the distribution
and seasonal occurrence of species in diverse habitats. Without these inventories
it is difficult to understand the changes that are often critical to the survival
of habitats.
The crane fly survey is funded by a grant from the Pennsylvania Wild Resources
Conservation Fund. This government program supports basic research and public education
related to the animals and plants of Pennsylvania, and is funded by income tax check-off
and sale of vehicle license plates.
Chen W. Young is associate curator of Invertebrate Zoology at Carnegie Museum
of Natural History.