BBC Wildlife - UK (2020-09)

T

hisspringa bizarre video filmed at

RaintownMeadows in County Durham

showeda great-crestedgrebe devouring a

sandmartin.Martin-hunting has been seen

atthewetlandseveraltimes in recent years,

generallyafterchillyweather forced nesting

martinstohawkforinsects low over the water.

AccordingtoPaulStancliffe of the British

TrustforOrnithology(BTO), this is virtually

unheardofingrebes,among the bird world’s

mostproficientfish-eaters. He suggests the

behaviourmightbe‘learned’, where only one

ortwoindividualshaveworked out how to

catchmartins.Alternatively, he says, it could

be‘opportunistic’,withthe grebe or grebes

simplycomingacrossa ditched sand martin

inthewater,butaddsthat would be pretty

rare.Grebesare,however, well known for

consumingfeathers,which they offer

totheiryoungandeatthemselves,

perhapstodealwithall

thosefishbones.

BenHoare

Why would a grebe catch birds?

Do all spiders have more or less round bodies?

ORNITHOLOGY

M

any do, yet there are

fascinating exceptions.

‘Harry Potter’ usually conjures

up images of wizards, children

in cloaks and banquet-style

meals, but the series has

also inspired the name

of a spider: Eriovixia

gryffindori, whose

tiny body

resembles a Hogwarts sorting

hat. The spider’s unusual shape

protects it from predators by

disguising it as dried foliage.

Adopting a non-rotund body

like this has worked for other

spiders too. Jumping spiders

in the genus Myrmarachne, for

example, have

turned their

abdomen

into what

looks like

two separate

body parts – a bit like wearing a

tight belt. The resulting ant-like

silhouette deters predators that

find ants noxious, and allows

ant-eating species to approach

their prey undetected. Such a

slimline body limits how many

eggs a female spider can lay.

A fat, round body clearly has

something going for it.

Sara Goodacre

ARACHNOLOGY

Samaraswillbegintofall

fromautumnonwards.

Treesenlistvariousforcesof

naturetoscatterseeds,from

hungryanimalstothewind,

gravity,water,evenfire.Some

usingwindassistancesealeach

seedinsideitsownpaperywing–

actuallya fruit,calleda samara.

Oftensamarasarejoinedinpairs,

suchasthetwirling‘helicopters’

ofsycamoresandmaples,orhang

bunchedin‘keys’,aswithashand

hornbeam.Englishandwychelms

alsoproducesamaras,though

theravagesofDutchElmDisease

(readmoreinWildMonth,p16)

meanchildrendon’tgettoplay

withthemmuchtoday.

BenHoare

Samara

Cockw

se

from

sp

der:

Ahmed

eta

.;A

amy;

Hugh

Pearson/naturep

.com;

Andy

Trowbr

dge/naturep

.com;

Markus

Varesvuo/naturep

.com;

Getty

Expelliarmus!The

shapeofEriovixia

gryndoriisits

magicweapon.

Sand martins (below)

are agile fliers and

make a rare but tasty

snack for a great-

crested grebe (right).

The Explainer

Q&A

84 BBC Wildlife