4.4.2). As with certain birds, some insects undergo
elevational migrations (see Sec. 4.5.2) and so require
the conservation of habitats at different altitudes. Many
aquatic insects are sensitive indicators of water qual-
ity (see Sec. 4.1), and can be used to monitor the health
of cloud forest streams (see Gill, "Impact of Monte-
verde Lecheria," pp. 446-447).
4.1. Aquatic Insects
4.1.1. Introduction
Paul Hanson
Insects that inhabit fresh water include orders that
consist almost entirely of aquatic species (Ephemerop-
tera [mayflies; Fig. 4.1], Odonata [dragonflies and
damselflies], Plecoptera [stoneflies], and Trichoptera
[caddisflies]) and groups that are predominantly ter-
restrial (Hemiptera ["truebugs"], Coleoptera [beetles],
and Diptera [flies, midges, and mosquitoes]). The larg-
est family of aquatic insects in Costa Rica is Chirono-
midae (Diptera), with perhaps 2000 species (C. de la
Rosa, pers. comm.). In contrast, Plecoptera are less
diverse in Costa Rica than in temperate regions, with
only one genus, Anacroneuria (Perlidae). Of the three
entirely aquatic orders, two are discussed below,
Odonata (see Sec. 4.1.2) and Trichoptera (see Sec.
4.1.3); the third major order, Ephemeroptera, is de-
scribed in Flowers (1992).
In most species, the larval stage is aquatic and the
adult stage is terrestrial. Exceptions occur in the aquatic
bugs and beetles, in which both stages are often aquatic.
Species of aquatic insects are often restricted to either
running or standing water and sometimes to certain
habitat types such as the water contained in tank bro-
meliads. Rapidly flowing water usually contains more
dissolved oxygen than stagnant water but has stron-
ger currents. In many cases, the terrestrial adults fly
upstream (Hynes 1970), which prevents the entire
population from being washed downstream.
Dragonflies, damselflies, most aquatic bugs, many
beetles, and other groups of aquatic insects may
be predators, herbivores, or detritivores. Functional
groups are based on their feeding mechanisms (Merritt
and Cummins 1996): shredders (living or decompos-
ing plant tissue), collectors (fine particulate organic
matter), scrapers (attached algae or living plant tissue),
piercers (living animal tissue), and engulfers (living
animal tissue). One of the few studies of feeding be-
havior of aquatic insects in Monteverde showed that
adult water beetles (Rhantus guticolis, Dytiscidae) and
dragonfly nymphs (Sympetrum nigrocreatum, Libellu-
lidae) preyed more heavily on tadpoles of the treefrog
Hyla pseudopuma (Hylidae) when the tadpoles were
small or in the four-legged stage; intermediate tadpoleFigure 4.1. Predatory mayfly from the Rio Guacimal on the Pacific slope below Monteverde. Photo-
graph by David Watson.96 Insects and Spiders