stages suffered less predation. However, another spe-
cies of dragonfly, Aeshna sp. (Aeshnidae), was able
to capture and kill all stages of tadpoles (Crump 1984).
Hunting strategies vary among species: Sympetrum
nigrocreatum waits in one place whereas Aeshna sp.
generally stalks its prey (Crump 1984).
Because most aquatic insects are restricted to cer-
tain types of water, they are good indicators of water
quality and are used in environmental impact stud-
ies (Rosenberg and Resh 1993). Such studies require
accurate identification, but few keys for the identifica-
tion of aquatic insects in Costa Rica exist. Keys to North
America genera (e.g., Merritt and Cummins 1996) are
only marginally useful.4.1.2. Dragonflies and Damselflies
of Costa Rican Cloud Forests
Alonso Ramirez
Dragonflies and damselflies (order Odonata) are the
best known of aquatic insects due to their large size,
brilliant colors, and conspicuous flight. Dragonflies
perch with their wings outstretched; damselflies rest
with their wings held together above the body. Adults
and nymphs are voracious predators of smaller in-
sects. Nymphs are aquatic and live in standing or
running water.
Fourteen families and 280 species of Odonata are
recorded from Costa Rica (Paulson 1982), although the
actual number is higher. Odonate diversity is great-
est in the lowlands and decreases with altitude. Sev-
enty species have been collected from areas above
1200 m, which represents 25% of the species in the
country. Of these, only 13 species are restricted to
altitudes above 1200 m. However, cloud forests have
not been well collected. Biogeography of the cloud
forest fauna indicates 41% of the species are of South
American origin, 28% are Central American (includ-
ing endemics), and 7% are North American. The rest
are widespread species whose origins are unclear.
Some odonate genera contain discrete lowland and
highland species. One highland species, Sympetrum
nigrocreatum, is probably derived from the wide-
spread mid-elevation species S. illotum. Philogenia
peacock! has only been found in cloud forests, whereas
P. carrillica is more commonly found at lower alti-
tudes. In the same stream, P. peacocki has been found
inhabiting the upper parts but is replaced by P. carril-
lica at lower altitudes, with some overlap of the two
species around 1200 m. Some cloud forests species
occur at intermediate altitudes (800-1500 m). For
example, Heteragrion majus, a characteristic inhab-
itant of streams in cloud forests, is also present at
lower altitudes (down to 800 m) in streams that share
characteristics with cloud forest streams such as high
humidity, steep slopes, and low temperature (17-
20°C). Of the species recorded from cloud forests,
60% have nymphs that live in open areas of lakes,
marshes, and ponds; 38% inhabit shaded streams;
and 2% live in specialized habitats such as brome-
liads and tree holes. These proportions depend on
the availability of the habitats. In general, open habitats
have been better studied than forest streams (Paulson
1982).
Nymphs are adapted to live in specific habitats, for
example, accumulations of dead leaves in riffles. The
most limiting factor is the availability of habitat suit-
able for nymph development. Most species tolerate
only narrow ranges of conditions such as temperature,
oxygen level, forest cover, types of aquatic vegetation,
and water pollution. They are good biological indi-
cators and their conservation depends on habitat pres-
ervation. Few species are well adapted to highly dis-
turbed habitats.4.1.3. Caddisflies of Costa Rican
Cloud Forests
Monika Springer
Caddisflies (Trichoptera) are a relatively small order
of insects that are closely related to the butterflies and
moths (Lepidoptera). Adults are not aquatic and are
seldom recognized due to their relatively small size
and inconspicuous colors. They resemble small moths
but lack a coiled proboscis; the wings are covered with
hairs rather than scales. Caddisfly larvae construct
portable cases from small stones or pieces of vegeta-
tion and are common in both standing and running
water in all types of microhabitats (MacKay and Wig-
gins 1979).
The first catalog of Costa Rican caddisflies (Hol-
zenthal 1988) included 174 species in 14 families. Over
450 species are now known from Costa Rica, of which
45% are new to science (R. Holzenthal, pers. comm.).
Most of these new species belong to the "microcad-
disflies" (family Hydroptilidae).
Cloud forests are characterized by cool running
waters, the types of streams believed to be the ances-
tral habitat of caddisflies (Ross 1956, Wiggins 1977).
Cool water has a higher oxygen tension than warmer
water and would be better suited for an organism
having only the minimum adaptation for aquatic life.
Among the typical mountain inhabitants, the holarctic
genera Limnephilus (Limnephilidae) and Lepido-
stoma (Lepidostomatidae) both reach the southern
limit of their distribution in Costa Rica and Panama.
Only a few species are known from Costa Rica; both
families are diverse and abundant in North America.
Caddisflies are divided into five groups based on
their case-building behavior (Wiggins 1977), all of97 Insects and Spiders