Effects of Pollution on
Natural Associations of Water Beetles!
FRANK N. YOUNG, Associate Professor of Zoology
Indiana University
Bloomington, Indiana
Individual species of water beetles are extremely variable in their reactions to pollution, either organic or industrial, and simple presence or
absence of species cannot generally be used to indicate contamination. Some
groups, however, such as the members of the family Elmidae, are extremely
sensitive to even mild pollution and quickly disappear from streams which receive even moderate amounts of industrial wastes (1). Others, such as the
larger Hydrophilidae and some Dytiscidae (4) may appear in small numbers in
grossly polluted waters but their occurrence in many cases seems to be correlated with the presence of unpolluted situations nearby from which they
migrate.
The most striking effects of pollution is in the changes in species composition and frequencies in the natural associations of*beetles which normally
occur in streams, empoundments or other natural situations. Since changes in
diversity of species and frequency can be determined roughly without laboriously identifying all of the species present, it may be possible to work out
relatively simple methods of assaying the effects of toxic pollutants and for
measuring recovery from pollution by sampling the beetle populations.
Water beetles have a number of advantages and disadvantages as indicators: They are abundant and diverse which allows many combinations of
species in different habitats. At the same time, this, together with the superficial similarity of many forms makes it difficult to determine them with
accuracy without undue effort. They occur in zones of streams, lakes, and
ponds which are readily accessible to sampling by simple wire strainers, dip
nets, or quantitative sampling devices, Figure 1. Conversely, they do not
usually occur in deeper water or on the bottom (except for larvae and adults
of certain Elmidae and Dryopidae) so that their use in large rivers is limited.
As already mentioned, some species of aquatic beetles are very sensitive
to pollution, and their presence may be used to indicate the purity of reservoir sources and other waters. Other species are less sensitive, particularly to
organic pollution, and may actually increase in moderately polluted streams.
Many adult beetles occupy situations in which the larvae do not occur, and
the adult association may be restored rapidly by migration after a disturbance.
A relatively few species, however, migrate so freely during the warmer
months that their occurrence in small numbers in any situation is indicative
only of the presence of a reflecting surface on which the beetles landed. For
example, freshly tarred roads or recently waxed cartops serve as well as water.
The greatest disadvantage is that in winter the beetles are inactive and
difficult to detect or trap. In Indiana, however, they can usually be successfully collected from mid-March through late November or even December.
1 Contribution No, 688 from the Zoological Laboratories of Indiana University, aided by grant RG6411 from the U.S. Public Health Service and grants
G-9, G-2708. and G-9229 from the National Science Foundation.
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