The New Neotropical Companion

Because three- toed sloths are usually observed in
cecropia trees, and clearly devour the leaves, for years
it was assumed that they ate only cecropia leaves. But
detailed studies in which radio transmitters were used
to follow sloths showed that they feed on leaves of
numerous tree species, moving to a different tree about
every day and a half. The problem is, when sloths are
not in cecropias, which offer easy views of the animals,
they are nigh impossible to spot.
Sloth populations are estimated to be five to eight
per hectare (2.5 acres) in Panama. This is considered

a high population density and is likely attributable to

their ability to ingest many kinds of leaves and tolerate

the defense compounds contained therein. Because

sloths have an extraordinarily low metabolic rate, they

do not eat as much as their numbers and body size (61

cm/24 in long, up to 4.5 kg/10 lb) might suggest. They

are relatively efficient digesters, owing their prowess to a

complex and long digestive tube and multitudes of gut

bacteria that process, ferment, and digest the leaves.

There are two species of two- toed sloths (genus

Choloepus; plate 16- 38). The two- toed is similar in

Sloths and Moths

As you know by now, tropical forests abound in unusual

species relationships. The sloth discussion mentioned,

for example, that numerous arthropods inhabit the fur

of sloths. These include moths. Yes, moths. At least five

moth species commonly inhabit sloth fur, presumably

feeding upon the algae that grow liberally within

the coarse, dense coat. The sloth- moth relationship

is commensal. The sluggish mammals do not appear

to gain any enhancement of probable survival and

reproduction from hosting the lepidopterans. But the

moths do gain fitness from inhabiting the sloth. They

have access to food— but that’s not all.

Sloth moths fly from the sloth’s fur when it descends

from the tree and defecates. The moths lay their eggs

directly on the sloth excrement. The moth larvae, or

caterpillars, feed on the sloth dung before pupating.

Once they metamorphose into moths, where do they go?

Why up into the canopy, of course, in search of a sloth to

inhabit. And not just any sloth will do. The relationship

has, at least in some cases, become evolutionarily tight.

For example, the moth Cryptoses choloepi is only found in

the fur of three- toed sloths, not two- toed.

The sloth’s habitat is forest, but to the sloth moth,

that is beside the point. Its habitat is a sloth or a sloth

dropping, depending upon whether it is an adult

or a larva. When you stop to think of the diverse

bacterial community within the sloth’s gut, indeed the

community that allows it to digest and thus to function,

and add to that the diverse community of algae and

animals that inhabit its fur, estimated to be in the

hundreds of species, the sloth, sluggish as it is, is one

impressive ecosystem.

Plate 16- 39. This three- toed sloth is holding its baby as it

sleeps on a branch. Sloth hair grows in a reverse direction

from the growth pattern in most mammals. Notice also the

distinctive green tinge to the mother’s fur, indicative of the

algal community that inhabits it. The baby has yet to acquire

its algae and thus is much browner. Photo by Dennis Paulson.

Plate 16- 38. Hoffmann’s Two- toed Sloth (Choloepus
hoffmanni). Photo by Gina Nichol.

336 chapter 16 from monkeys to tarantulas: endless eccentricities