the two whirl and trade blows at a 
breathtaking pace. In the accounts 
of such fights that I tape-recorded 
as part of my research, I frequently 
sound like a sportscaster. As a pair 
of fighting mantis shrimps performed 
as many as 500 different aggressive 
acts during a ten-minute bout, student 
friends rooted for favorite warriors. 
Extreme aggression creates social 
problems for the mantis shrimps. Like 
all crustaceans, they must shed their 
hard outer skeleton in order to grow. 
During the molting period, the 
shrimps are immobilized, soft, and 
thus vulnerable to predators, particu- 
larly other mantis shrimps. In fact, 
cannibalism of newly molted shrimps 
is common if the molted individuals 
have no refuge. Nevertheless, mantis 
shrimps have developed a variety of 
adaptations that decrease the dangers 
associated with molting, including 
sealing their burrow entrances with 
pebbles; a reduced period of incapaci- 
tation compared to other, less aggres- 
sive crustaceans; molting late at night 
when other mantis shrimps are inac- 
tive; and synchronous molting (in as- 
sociation with lunar cycles). 
Their aggressive behavior also im- 
poses a solitary existence upon mantis 
shrimps, except for a brief mating pe- 
riod when males and females manage 
to live together. Males apparently 
probe various burrows until they find 
a female sufficiently receptive to per- 
mit their entrance. Courtship is an 
elaborate affair, replete with threat 
displays that involve exposing the spe- 
cies-identifying eyespots. Aggressive 
acts, such as lunges and strikes, and 
defensive coiled stances gradually di- 
minish as the pair become conditioned 
to each other by courtship displays 
and body contact in which the two 
glide past euch other in the burrow, 
their sides touching. Before mating, 
the male massages the female’s back. 
During copulation, he constantly 
scratches her anterior thorax with a 
small, brushlike first maxilliped. 
Courtship and mating continue in the 
burrow for several days until overt 
Charles R Seaborn 
aggression reappears; eventually, the 
female evicts the male from the bur- 
row. 
In the next few days the female 
lays a batch of eggs (ranging from 
fewer than a hundred eggs in some 
small species up to many thousand 
in large species); then for more than 
a month she will abstain from food 
while she carries the compact mass 
in her maxillipeds. By constantly 
kneading and cleaning her brood, the 
female protects the developing em- 
bryos from microorganisms that would 
foul and kill them if she abandoned 
the egg mass for more than a few 
hours. The small larvae hatch and re- 
main with the female in her burrow 
for several days to a week before they 
emerge and swim away. Like many 
other tiny organisms subject to pre- 
dation by plankton-eating fishes, the 
transparent, spiny mantis shrimp lar- 
vae migrate to the surface to feed 
when the fishes are less active, just 
after sunset and before dawn; during 
the day the larvae hide near the sub- 
strate. The larvae bear raptorial spear- 
ing claws, and prey on other, smaller 
nocturnal plankton. 
The evolution of the intense aggres- 
sive behavior of mantis shrimps has 
Polychaete worms, such as 
Hermodice carunculata, right, share 
the same coralline habitats as mantis 
shrimps. Crabs of the family 
Majidae, below, are common prey 
for mantis shrimps living in coral 
reef rubble and back reef habitats. 
been linked to their occupation of bur- 
rows. Most fighting occurs in and 
around burrows, suggesting that they 
are a critically important and limited 
resource; when the shrimps venture 
forth from their protective burrows 
they are subject to predation by fishes. 
As might be expected, then, those spe- 
cies of mantis shrimps that inhabit 
preformed holes in dead coral or rocks 
are more aggressive than species that 
dig burrows in mud or sand and need 
not depend on an existing supply. 
Larger holes in coral are less common 
than smaller ones, and larger individ- 
uals within stomatopod species have 
also been observed to be more ag- 
gressive than smaller individuals. 
Similarly, among related coral-dwell- 
ing species of mantis shrimps, larger 
species are often more aggressive (and 
have brighter-colored spots) than 
smaller species. 
Mantis shrimps that dig burrows 
must spend considerable time and ef- 
fort in excavating, all the while ex- 
posing themselves to predators. Thus, 
these burrows are costly and, like pre- 
formed ones, worth defending. As a 
result, even shrimps that live in ex- 
cavated burrows in soft substrates are 
considerably aggressive, although ag- 
40 
