Eco-ethology of Brachytrupes megacephalus

Department of Biological, Geological and Environmental Sciences,
University of Catania, Italy. Section of Animal Biology “Marcello La Greca”
Via Androne 81 - 95124 Catania (Italy)
E-mail: [email protected]
Summary
B. megacephalus, described by Lefebvre (1827) on specimens from Sicily, is a south Mediterranean species diffused in sandy environments of Sicily, Aeolian Islands, Maltese Islands, southern Sardinia, North Africa (included
the Saharan oases). South of Sahara this species is substituted by B. membranaceus (Drury).
The authors summarize the researches on the behavioural ecology of Brachytrupes megacephalus carried out
since 1982 in Sicily by the eco-ethology laboratory of the Department of Biological, Geological and Environmental
Sciences, University of Catania.
Key words: biological cycle, behavioural ecology, sandy environments, eco-touristic resources.
In the past years B. megacephalus has been persecuted (and it still happens in many territories) by farmers on account of damages that it cause to the crops (Leonardi, 1901; Grandi,
1911, 1951; Silvestri, 1939; Damiano, 1962): due to its current rarefaction in Europe, this
species has been included in the Annexes II and IV of EU Directive 92/43 as species requiring strict protection.
The biology of B. megacephalus was studied by Forel (1893) and Valdeyron-Fabre
(1955) in Tunisia, by Scortecci (1971) in Libya and subsequently by some of us in Sicily
(Caltabiano et al., 1982).
This cricket (Fig. 1), vegetarian, hygrophilous, homocromous with the substrate, crepuscular and nocturnal, has considerable morphological (Chopard, 1938) and behavioural
characteristics including special adaptations for swimming and digging (Caltabiano et al.,
1979) and for reproduction.
It is a burrowing animal that lives in tunnels (more superficial and articulated in spring,
more deep and linear in winter, as showed in Fig. 2) realised in the sandy soil: the tunnel
communicates to the surface by an opening morphologically different in the two sexes (Fig.
3). Particularly impressive is the pattern of sand expulsion during the tunnel excavation. This
action produces typical little, irregular sandy cones (Fig. 4) (reaching even 13-15 cm in height),
visible on the ground surface: the sand expulsed on the surface from inside closes the tunnel
during the underground activity of the animal.
B. megacephalus has an annual life cycle with breeding season placed normally between
mid-March and late April; each male, generally around sunset, attracts females (1-2 in the
same evening) in his lair by intense sounds produced by rubbing, one against the other,
special ribs placed on the fore wings; the male calls are amplified in a small widening created at the mouth of the lair (Fig. 5) which acts as a resonator (females are silent and waits
in their lairs whose opening lacks widening); the sound is very ear-piercing and audible
at a considerable distance. The female, moving away from her burrow, is able to reach a
male performing his calling song by phonotaxis. Mating normally occurs within the male’s
burrow and consists in the application, by the male in the female genital tract, of a garish
spermatophore (Fig. 6). After mating the females are “segregated” in lateral branches of
the main tunnel, as it happens in B. membranaceus (Costa et al., 1987; Costa e Petralia,
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Erminia Conti, Giovanni Costa, Alfredo Petralia, Ettore Petralia
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Eco-ethology of Brachytrupes megacephalus
(Orthoptera, Gryllidae), protected species in UE
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1990) (Fig. 7), where they lay eggs in clutches (40-60 per clutch): after spawning, the female
opens a new gateway to the outside (Fig. 8).
The number of cones observed on the surface of the sand is an indicator of the reproductive
activity (Fig. 9): generally there is a peak around mid-April, while highly variable climatic
conditions can cause slowdowns or suspensions of the activity.
At the end of the breeding season, during which the animals do not feed, adults die. The
young (wingless) (Fig. 10) appear in June and are very numerous (and produce cones in a very
high number) (Fig. 11), but only few of them will survive and reach the next breeding season
due to the high mortality during the post-embryonic development. After the early autumn rains
the neo-adults manifest their presence by the large sand mounds produced excavating their
burrows. In the same season the animals, grown up and become winged, feed very intensively
before stopping their surface activity just before winter. Completed the hibernation, the animals
will devote themselves exclusively to reproduction.
In some Sicilian nature reserves (“Macchia Foresta del Fiume Irminio”, “Isola di Capo
Passero”, “Oasi Faunistica di Vendicari”, “Oasi della Foce del Fiume Simeto”), by detecting
sandy cones and burrow openings, the localization of the species within the protected areas
has been mapped (Petralia et al., 2003; Russo et al., 2006).
As regard to the animal size, some of us carried out a comparison between males from
Marina di Ragusa (Sicily) and males from Douz (Tunisia): in the latter station, located more
south than the first one, the animals were larger (Tab. I).
Marina Ragusa
A
B
C
D
E
arithmetic mean
1.38
1.25
0.60
1.90
0.54
standard dev.
0.23
0.06
0.09
0.06
0.02
A
B
C
D
E
arithmetic mean
1.43
1.35
0.69
2.11
0.57
standard dev.
0.09
0.01
0.08
0.13
0.06
Douz
Tab. I –Size comparison between specimens from Sicily (up) (sample of 25 males) and Tunisia (sample of 38 males). A: maximum width of the head; B: maximum width of the pronotum; C: minimum width of the pronotum; D:
maximum length of the back femur; E: maximum width of the back femur (Inclimona, 2006).
The information concerning the biology, the eco-ethology and the territorial localization
of the species, are basic tools for its correct management and conservation by means of the
protection of the specific cricket environment: in particular, inside the protected areas, this
is useful in the identification of appropriate tracking pathways in order to prevent the indiscriminate and anarchic stamping on sandy soil (both by humans and vehicles) which causes
an heavy impact on the substrate and consequently on the animals.
Ultimately B. megacephalus is characterized as an element of the biodiversity of particular interest thanks to its complex eco-biology: its protection requires the preservation
of the sandy habitats in which the cricket is highly specialized. It is also an animal whose
behavioral performance can be an eco-touristic resource for the biowatchers, which can be
targeted also on elements of the so-called “minor fauna” but no less attractive and intriguing,
as B. megacephalus is.
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Fig. 2 - Wax casts of tunnels. On the left: example of spring burrow; on the right: example of winter burrow.
Fig. 3 – Entrances of the burrows. On the left, a typical male’s hole widening; on the right, a female hole.
Fig. 4 - Examples (left and right) of irregular little sandy cones produced by the digging activity: the sand is expulsed
on the surface from inside.
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Fig. 1- Specimens of Brachytrupes megacephalus: on the left, a silent female; on the right, a male with the stridulatory organ on its forewings.
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Fig. 5 - Scheme representing the male positioned in the widening at the entrance of
its hole calling for females (on the right).
Fig. 6 – On the left: a male with the extruded spermatophore at the extremity of its abdomen. On the right the mating
position: the female mounts the male.
Fig. 7 – After mating the male closes the entrance of its burrow realizing the sandy
cone: the females are individually “segregated” in branches of the burrow.
Fig. 8 – After spawning each female realizes a new tunnel toward outside and leaves
the burrow of the male.
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Fig. 10 – Left: a new born cricket (few days old), wingless. Right: nymph (about 1.5-2 month old) with rudimentary
wings.
Fig. 11 – Trend in the number of sandy cones (y axis), observed in the sample area
mentioned in Fig. 9, by the appearance of young up to the cessation of activity in the
late autumn (x axis).
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Fig. 9 – Trend in the number of sandy cones (y axis) observed in 2008 from mid-March
to early May during the reproductive period (x axis) in a sample area of 100 square
meters in the Natural Reserve “Macchia Foresta del Fiume Irminio” (Ragusa, Italy)
(Battaglia, 2008).
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