Observations on the larval morphology of the Antlion Myrmeleon bore (Tjeder, 1941) (Neuroptera Myrmeleontidae) and its life cycle in the Po Valley (northern Italy)

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59
Ann. Mus. civ. St. nat. Ferrara Vol. 8 2005 [2007] pp. 59-66 ISSN 1127-4476
Observations on the larval morphology of the Antlion Myrmeleon
bore (Tjeder, 1941) (Neuroptera Myrmeleontidae) and its life cycle
in the Po Valley (northern Italy)
Rinaldo Nicoli Aldini
1, 2
1) Istituto di Entomologia e Patologia vegetale, Facoltà di Agraria, Università Cattolica del Sacro Cuore, via Emi-
lia Parmense 84, I – 29100 Piacenza (Italy); 2) Scienze degli Alimenti, Polo Scientifico-Didattico di Cesena della
Facoltà di Agraria, Alma Mater Studiorum, Università degli Studi di Bologna, Piazza Goidanich 60, I-47023 Ce-
sena (Italy), e-mail: rinaldo.nicoli@unicatt.it
Myrmeleon bore (Tjeder), an Eurasian antlion, has hitherto been recorded only in few locali-
ties of northern Italy, the southernmost part of its range. The author carried out observations in
the Pavia province (western Po Valley) and rearings of this species, in order to obtain data con-
cerning larval morphology, ecology and ethology, as well as to study its life cycle. Field observa-
tions and laboratory rearings indicate that the life cycle of M. bore in northern Italy may be com-
pleted in one year. The morphological characteristics of its three larval stages are noted and il-
lustrated by SEM micrographs, discriminating them from those of the very similar and syntopic M.
inconspicuus Rambur.
Key words – larval taxonomy, SEM, geographic distribution, voltinism, myrmeleontids.
Introduction
Myrmeleon bore (Tjeder, 1941) (Neuro-
ptera: Myrmeleontidae), an Eurasian antlion,
occurs in Europe mostly in the central and
northern regions (Ohm, 1965; Aspöck et al.,
1980, 2001; Letardi, 1998; Röhricht, 1998);
in Italy it has hitherto been recorded very
rarely and only in the North (Aspöck &
Aspöck, 1969; Nicoli Aldini, 1983; [Bernardi]
Iori et al., 1995; Hellrigl & Hölzel, 1996). Field
studies in the Lomellina area (Province of
Pavia, Lombardy) and laboratory rearings
have been carried out by the author, since
the seventies, for obtaining data on the eco-
logy, behaviour and life cycle of this species.
Observations have also been conducted u-
sing a scanning electron microscope in order
to depict the morphological characteristics of
its larval stages and differences between
them and the corresponding stages of the
very similar and syntopic M. inconspicuus
Rambur, 1842. The mature larva of the latter
was described masterfully by Principi (1943);
taxonomical characteristics of the larva of M.
bore were summarily presented by Friheden
(1973), other illustrations are to be found in
Dobosz (1993) and Ábrahám (1995).
Materials and methods
After the first findings of M. bore larvae in
the Lomellina area, the research was widened
to other stations in this region; moreover, some
collections were examined to obtain further
data on the presence and distribution of this
antlion species in Italy.
The observations and samplings of larvae
of M. bore and other antlions digging pits, were
made in the Lomellina area during a period of
nearly thirty years (1977 to 2005), in June-July
and September-October. Laboratory rearings
were conducted in Bologna, in an uncondi-
tioned environment.
Larval specimens were examined alive and
shortly before death, as well as specimens
preserved in ethanol 70-75%, dry specimens
and cast skins from 1st and 2nd instar larvae,
in order to study larval morphology. SEM mi-
crographs were carried out in the Electron Mi-

Proceedings of the IX International Symposium on Neuropterology
60
croscope Laboratory of the Faculty of Agricul-
ture, Università Cattolica, Piacenza, employing
both non-metallized and metallized dry mate-
rial, by means of a SEM Philips XL30 ESEM.
Measurements of total larval length were con-
ducted on live specimens; measurements of
larval head (Fig. 3B) were conducted on
specimens preserved in ethanol 70-75% (12
specimens for each stage of each species
were examined), by means of a Leica Wild M
10 stereoscope, using an ocular micrometer.
Other observations on larval morphology were
carried out on prepared parts or appendages,
previously clarified in KOH and mounted on
slides in Faure’s fluid. The “digging-setae” lay-
out patterns of the 9th sternite and their rela-
tive frequencies were observed by examining
a total of 263 M. bore larvae (L1: 69, L2: 150,
L3: 44) (Tab. II) and 392 M. inconspicuus lar-
vae (L1: 27, L2: 256, L3: 109). Detailed data
on the latter species will be published in a fu-
ture paper.
Results
Distributional data for M. bore
M. bore larvae were found in various
localities of the southeastern Lomellina
area (Pavia), both along river beds, and
in some zones of the inland plain: a)
Mezzana Rabattone, Po river; b) Pieve
Albignola: Cascinotto Mensa, Po river; c)
Pieve Albignola, Terdoppio stream; d)
Pieve Albignola to Scaldasole: sandy
banks and oak-wood borders near Ca-
scina Rossa (now demolished) and Ca-
scina Paralupo; e) Scaldasole, locality “I
Dossi”: borders of a small oak-wood; f)
Alagna. In the collections of the Istituto di
Entomologia, Università Cattolica, Pia-
cenza, 3 adults of this species are pre-
served, labelled as follows: Cremona,
Pizzighettone, farm “La Tencara”,
19.VII.1970, light trap (1 female); Piacen-
za, 28.VII.1989 (1 male); Piacenza, Po
river, VI.1991 (1 male). M. bore therefore,
as published up to now, occurs in three
Italian regions: Alto Adige (Aspöck &
Aspöck, 1969; Hellrigl & Hölzel, 1996),
Lombardy and Emilia (Nicoli Aldini, 1983,
and present data) (Fig. 1).
Larval morphology of M. bore
1st instar larva (L 1)
Colouring – Basic colouring whitish straw,
dorsally tending towards beige, with several
brown or dark brown spots and blotches dor-
sally and ventrally (Fig. 2, Fig. 3A) (newhat-
ched larva with only the cephalic and some,
more or less evident, thoracic and abdominal
spots). Head capsule dorsally almost entirely
dark brown, due to the presence of large and
confluent spots in the fronto-clypeal and epi-
cranial areas (the epicranial spots extending to
the sides); ocular tubercles black; head cap-
sule also with a dark spot on each side poste-
riorly; ventrally yellowish brown with a pair of
large and shaded brown spots in the hy-
postomal areas. Antenna dark brown. Mandi-
ble and maxilla iron-brown; labial palp with the
last segment darker. Legs light, without spots,
pretarsal claws of metathoracic legs clearly
iron-coloured.
Size – Total length (including jaws) 3.8 (new-
hatched larva) to approx. 6 mm; morphometri-
cal data of the head: Tab. I.
Relevant morphological features –
Black setae, of various shapes and sizes, scat-
tered almost all over the body; the fine struc-
ture of some of them from the anterior margin
of the head, with longitudinal series of short
spinules, is shown in Fig. 4A. Delicate white
sinuous filaments (detail in Fig. 4C) dorsally
scattered almost all over the body, latero-
ventrally over thorax and abdomen. Head cap-
sule longer than broad, with maximum width at
the ocular tubercles. Antenna (Fig. 4D) 11- to
15-segmented (scape stout, pedicel and apical
flagellomere more or less elongate). Mandible
falcate, tridentate, slender and finely sharp-
Fig. 1 – Myrmeleon bore, Italian distribution (biblio-
graphic data and author’s data); inside the circle:
stations in the Lomellina area.

R. Nicoli Aldini – Observations on the larval morphology of Myrmeleon bore (Tjeder, 1941)
61
Fig. 2 – Myrmeleon bore: 1st, 2nd, 3rd instar larva (R. Nicoli Aldini del.).
ened, longer than the cephalic capsule; labium
(Fig. 4E) with palps 3-segmented. Thoracic
spiracle: Fig. 4F. “Digging setae” of the 9th
sternite: Fig. 3C-D, Fig. 4G, Tab. II. Their most
frequent pattern comprises 8 setae in the pos-
terior row (4 on each side, forming the struc-
ture named “palette” by Steffan (1975), in
which the most lateral seta is longer and
sharpened), near the hind margin of the ster-
num; 4 setae in the row immediately in front;
and 2 in front of them, in the discal area of the
sternite, placed side by side or asymmetrically,
more or less distant from each other. Some-
times there is only one or none of the latter.

Proceedings of the IX International Symposium on Neuropterology
62
Tab. I – Myrmeleon bore and M. inconspicuus, measurements of the head and number of antennal segments
(12 specimens were measured and examined for each larval stage of each species).
Myrmeleon bore Myrmeleon inconspicuus
Measurements (mm)
L 1 L 2 L 3 L 1 L 2 L 3
Head length (incl. jaws) 1.77-1.93 2.65-2.92 4.16-4.62 1.46-1.64 2.10-2.35 3.20-3.77
Length of the head capsule 0.84-0.92 1.28-1.45 2.06-2.26 0.68-0.81 1.05-1.17 1.62-1.90
Width of the head capsule 0.75-0.81 1.12-1.26 1.71-1.90 0.64-0.75 0.94-1.07 1.45-1.71
Number of antennal seg-
ments
11-15 8-14 9-15 11-15 13-16 10-15
Tab. II – Myrmeleon bore, layout patterns of “digging setae” on the 9th sternite, and their relative frequencies for
each larval stage and for the whole number of larvae examined.
Layout patterns
of the “digging
setae”
L 1
(69 larvae
examined)
L 2
(150 larvae
examined)
L 3
(44 larvae
examined)
L 1 + L 2 + L 3
(263 larvae
examined)
2 (asymm.) – 5 – 7 - 1 (0.66%) - 1 (0.38%)
2 (asymm.) – 3 – 8 - 1 (0.66%) - 1 (0.38%)
0 – 4 – 8 5 (7.25%) 5 (3.35%) - 10 (3.80%)
1 – 4 – 8 9 (13.04%) 11 (7.35%) 4 (9.09%) 24 (9.13%)
2 (asymm.) – 4 – 8 42 (60.87%) 109 (72.66%) 31 (70.46%) 182 (69.20%)
2 (symm.) – 4 – 8 11 (15.94%) 13 (8.66%) 4 (9.09%) 28 (10.65%)
3 (asymm.) – 4 – 8 - 7 (4.66%) 5 (11.36%) 12 (4.56%)
1 – 5* – 8 2 (2.90%) 3 (2.00%) - 5 (1.90%)
* symmetric (i. e. in one row) or asymmetric but close to each other.
Tab. III – Morphological features discriminating Myrmeleon bore and M. inconspicuus larvae.
Species/Characteristics Myrmeleon bore Myrmeleon inconspicuus
SIZE Slightly larger (see Tab. I for the
head).
Smaller (see Tab. I for the head).
MANDIBLE Relatively longer, more slender
distally; in all stages, mandible a
little longer than the head capsule.
Relatively shorter, less slender
distally; only in L 1 mandible longer
than the head capsule.
L
ABIAL PALP 3-segmented (see Fig. 4E). 4-segmented.
T
HICK CEPHALIC SETAE With longitudinal series of short
spinules (evident mainly in 1st in-
star larva, see Fig. 4A).
With longitudinal series of slightly
longer and thinner spinules (evi-
dent mainly in 1st instar larva, see
Fig. 4B).
N
UMBER AND LAYOUT OF “DIGGING
SETAE
” ON THE 9TH STERNITE
Intermediate group forming a row
of 4 setae (only exceptionally 5);
anterior (discal) group comprising
0-3 setae (see Fig. 3C-F, Fig. 4G,
and Tab. 2).
Intermediate group consisting of at
least 6 setae (only exceptionally 5,
not rarely 7, rarely 8-9) disposed in
more or less regular row; anterior
(discal) group comprising 0-7 setae
disposed more or less irregularly
(see Fig. 3G-I).

R. Nicoli Aldini – Observations on the larval morphology of Myrmeleon bore (Tjeder, 1941)
63
2nd instar larva (L 2) (main differ-
ences in comparison with L1)
Colouring – Dark colouring of the head cap-
sule generally a little less wide than in L 1, with
large dark spots dorsally (Fig. 2) and a dark
spot on each side posteriorly; ventrally with a
pair of oval dark spots.
Size – Total length (including jaws) approx. 6-
8 mm; morphometrical data of the head: Tab. I.
Relevant morphological features – Ma-
ximum width of the head capsule a little behind
the ocular tubercles. Antenna 8- to 14-
segmented. Layout pattern of “digging setae”
of the 9th sternite rather variable (Tab. II), their
more frequent settings correspond to the 2
(asymmetric or symmetric) – 4 – 8 type.
3rd instar larva (L 3) (main differ-
ences in comparison with L 2)
Colouring – Head capsule dorsally with one
frontoclypeal dark spot and some symmetric
epicranial dark spots, less wide than in L 2
(Fig. 2); on each side with a dark spot poste-
riorly; ventrally with a pair of dark spots with
shaded margins in the hypostomal areas. An-
tenna uniformly brown or yellow ochre, with the
last segment darker; mandible yellow ochre,
gradually darker in the points.
Size – Total length (including jaws) approx.
8.5-12.5 mm; morphometrical data of the head:
Tab. I.
Relevant morphological features – An-
tenna 9- to 15-segmented (only 6 segments in
both antennae, with various flagellomeres
fused together, in an anomalous specimen).
Spinosity of the ventral side of the mandible:
Fig. 4H. Layout pattern of “digging setae” of
the 9th abdominal sternum rather variable (Fig.
3E-F, Tab. II), their more frequent settings as
in L 2.
Through the development from L1 to
L3, therefore, the dark colouring of the
head decreases in width; the mandible is
dark in L1 and L2, lighter in L3. The head
capsule modifies its shape a little and re-
mains slightly shorter than the mandible.
On the 9th sternite, the “digging setae” of
the discal group tend to increase in num-
ber (in L3, not rarely 3 setae, placed
asymmetrically, are to be found) (Tab. II).
Fig. 3 – Myrmeleon bore: A, schematic distribution of ventral spots in 1st instar larva; B, technique of measure-
ment of larval head (htl = total length of the head; hcl = length of the head capsule; hcw = width of the head
capsule); C-F, some layout patterns of “digging setae” of 9th sternite in 1st (C: 0-4-8; D: 1-4-8) and 3rd (E: 2-4-
8; F: 3-4-(7)8) instar larva. M. inconspicuus: G-I, idem in 1st (G: 2-6-8; H: 3-7-8) and 3rd (I: 4-8-8) instar larva.
(Various magnification; R. Nicoli Aldini del.).

Proceedings of the IX International Symposium on Neuropterology
64
Fig. 4 – A, Myrmeleon bore, L 1: detail of two setae on the anterior margin of the frontoclypeal region; B, ditto of
Myrmeleon inconspicuus, L 1; C, M. bore, L 1 (cast skin): detail of a delicate sinuous filament from the thoracic
perispiracular region, at high magnification; D, M. bore, L 1: antenna. E, M. bore, L 1: labium; F, M. bore, L 1
(cast skin): thoracic spiracle; G, M. bore, L 1: 9th abdominal sternite; H, M. bore, L 3: ventral detail of mouth-
parts (inside the circle: spinosity of the ventral side of the mandible). (SEM photos).

R. Nicoli Aldini – Observations on the larval morphology of Myrmeleon bore (Tjeder, 1941)
65
Tab. IV – Myrmeleon bore, number and percentages of the three larval stages in three subsequent samplings
made in the span of twelve months in the same poplar grove with sandy soil, at Pieve Albignola near Terdoppio
stream (Province of Pavia), years 1983-1984.
Larval stage
1.X.1983
(89 larvae)
1.VII.1984
(25 larvae)
28.IX.1984
(61 larvae)
L 1 23 (25.8%) 0 (0.0%) 31 (50.8%)
L 2 62 (69.7%) 2 (8.0%) 30 (49.2%)
L 3 4 (4.5%) 23 (92.0%) 0 (0.0%)
Almost all over the body, black setae of
various shapes and sizes, as well as deli-
cate white sinuous filaments, increase in
number.
Some morphological characteristics
discriminating between M. bore and M.
inconspicuus larvae are summarized in
Tab. I (head measurements) and Tab. III.
Bio-ecological notes, life cycle
duration
Only a short account can be reported
here. In the southern Lomellina area, M.
bore occurs in various localities, in envi-
ronments with suitable sandy soil: the
banks of the Po river bed, the poplar gro-
ves near this major river and its tributaries,
and the sandy banks (the typical “dossi” of
the Lomellina area, with the surviving
small oak-woods (Quercus pedunculata),
associated with the invasive robinia (Ro-
binia pseudacacia) and a few other spe-
cies of trees) in the inland agricultural
plain. In all these environments, this ant-
lion is syntopic with M. inconspicuus,
which is generally more abundant, only
rarely the larvae of these two species we-
re found in similar percentages. The pits
of M. bore are located in the same places
as those of M. inconspicuus, in bare soil
or, especially for the pits of the 1st and
2nd instar larvae, which are closer toge-
ther, near the base of herbs and small
shrubs, in any case in sunny places. Syn-
topy with Myrmeleon formicarius Linné,
1767 and Euroleon nostras (Geoffroy in
Fourcroy, 1785) (both, but especially the
latter, scarcer than the other two species)
was observed in some environments such
as sandy banks in the inland plain, near
small oak woods (Nicoli Aldini, 1983), and
on a sandy slope far from rivers. These
four species display partially different pre-
ferences in the location of their pits. The
pits of E. nostras, for instance, are always
found under overhangs – as has been well
known for many years, see e.g. Steffan
(1975), Yasseri & Parzefall (1996). It is
likely that M. bore larvae, as well as those
of M. inconspicuus (Steffan, l.c.), are able
to survive the prolonged submersions of
the sand banks of the Po river bed, which
occur in some periods of the year.
Field samplings and laboratory rea-
rings in climatic conditions similar to those
of the natural habitat indicate that the life
cycle of M. bore in the Po valley may be
completed for the majority of the indivi-
duals in one year, compared with 2-3 ye-
ars in central Europe (Hölzel, 1973; Gepp
& Hölzel, 1996; Hölzel & Wieser, 1999).
This fact in the Lomellina area is demon-
strated by the high number of 3rd instar
larvae of M. bore in July and their low
number or absence in September-
October, as well as by the very low num-
ber of 1st and 2nd instar larvae in July and
their abundance in September-October
(Tab. IV). Only a small number of larvae
takes two years (personal observations),
as has also been found for M. inconspi-
cuus (Principi, 1943; Steffan, 1975; Panta-
leoni, 1982; Nicoli Aldini, unpublished da-
ta). In the laboratory rearings, M. bore a-
dults started to emerge in the first ten
days of June, ending in the second ten
days of August. During field research in
the Lomellina area, in June-July adults of
this species were never found (maybe

Proceedings of the IX International Symposium on Neuropterology
66
they emerge later or are scarcer), where-
as some specimens of M. inconspicuus
were captured in July on herbaceous
plants.
Acknowledgements
The author thanks Mr. Andrea Roverselli,
Laboratorio Microscopia Elettronica, Facoltà di
Agraria dell’Università Cattolica, Piacenza, for
his technical assistance, and Dr. Robert Gü-
sten, Naturgeschichtliche Abteilung, Hessi-
sches Landesmuseum Darmstadt, for his va-
luable suggestions and comments on the ma-
nuscript.
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