Insects and spiders less likely to survive in tropics,
new research shows
Last updated on 10/31/2016 Print this page
Tropical insects and spiders left unprotected by their parents
are far more likely to be killed by predators than bugs in colder
New research by academics at the University of
Hull and the University of Sao Paulo in Brazil shows the mortality
of unguarded broods is significantly higher in warmer and wetter
climates where predators and parasitoids are more active.
Appearing in the journal Biological Reviews,
the research also shows the survival of broods left home alone
increases significantly when parents build extra defences to
protect their young when they are not around, such as silk egg
sacs, sticky coatings or nests.
The results also help to explain why parental
care is more common in tropical species.
James Gilbert, a lecturer in Zoology at the
University of Hull involved in the study, said:
In arthropods, activity is linked to temperature –
predators and parasitoids are more active in the tropics because it
Parental care protects against these natural enemies,
so in theory the benefits of this behaviour should be higher in
When we tested this prediction by comparing the
mortality of guarded and unguarded broods in arthropods, we found
that the mortality of unguarded broods was higher, and parental
care was more beneficial in warmer, less seasonal
The research backs up a hypothesis dating back more
than 40 years that parental care in arthropods evolved in response
to predation in tropical rainforests. While that’s been assumed to
be true for many years, this research now provides
In the insect world, offspring attendance
(remaining with young after hatching) is a common way of protecting
Previous researchers have noted that
experimentally removing arthropod parents of various species
“condemns the offspring to death”, mostly due to attacks from
predator and parasitoids - rogue insect robbers that hijack and
consume eggs and larvae.
In the new research, entitled “Macroecology of
Parental Care in Arthropods”, a team of experts from the University
of Hull and the University of Sao Paulo in Brazil took these past
authors’ data and systematically compared them, looking for a link
between mortality and climate.
The researchers also looked at the impact of
additional defences on mortality rates and found that where
parental care and additional defences were combined, the
differences in mortality between warm and wet and cold and dry
climates largely disappeared.
Despite the threat posed by natural enemies,
many parents occasionally have to leave their offspring temporarily
unguarded, whether it’s to catch prey to eat themselves or get food
for their offspring. Some arthropod species have developed backup
defences to keep home-alone broods safe.
Mr Gilbert said:
The combined message is, tropical arthropod broods with
no other defence than parental care are highly likely to be killed
when left unattended by their parents, whereas in a temperate
climate the eggs are less likely to be trashed.
However, if parents have extra defences, they can
afford to leave their brood to go off and feed, even in tropical
Although you don’t normally think about arthropods as
caring parents, many of them love their children too.
The assassin bug
The assassin bug is very unusual in the insect
world in that it’s the dad who guards the eggs from predators and
parasitoids, while the mum goes off and lays more eggs.
Found in Uganda, assassin bugs are ambush
predators that prey on other insects. The major threat to their
eggs is from parasitoid wasps.
While the stay-at-home dads may sound like
enlightened creatures, their behaviour has an ulterior motive:
females of their species are attracted to males that already have
The assassin bug father doesn’t build any
additional defences to allow it to go off and feed. Instead he
sustains himself by eating some of his own eggs.