EXAMPLES OF THE DIFFERENCE BETWEEN MALE AND FEMALE PUPAE
© REG FRY 2014
In most cases the sex of a moth pupa can be determined from markings or indentations on the ventral side of the pupa. With many of the larger pupae it is often easy to be certain, particularly if you have a number of pupae which include both sexes.
The general rule is that you count along four segments from the segment containing the wing cases (to the segment marked S4 below) and if there is no black line or slot in the middle of that segment but there is a kidney-shaped bump on the fifth segment (S5) with a black slot in the middle of it, then it is a male. In some cases the kidney shape looks more like two small bumps either side of the black slot. With the majority of species the legs finish on or just after the segment with the wing cases, however with some such as the Burnished Brass the legs extend well over the S1 segment.
If it is a female pupa then there is a slot in the middle of the fourth segment (S4) - see the example below. With some species the border of the S4 segment which is nearest to the cremaster is curved inwards. This pupa has one of the most extreme and very obvious slopes inwards. The degree and amount of curvature varies considerably, with some species it is very slight. The position of the female slot also varies considerably, with some species it straddles the fourth and fifth segments, in others it is in two parts one part on the fourth segment and one on the fifth. However the general rule still applies with all the pupae that I have seen - if the segment S4 has no sign of a slot and there are two bumps either side of a slot on S5, the pupa is male.
With some species it is difficult to know which is the first segment (S1) to start counting from. In these cases it in necessary to turn the pupa over and work out which segments are Abdominal segments 8 and 9 (equal to S4 and S5 in this example).
The same rule also applies to many butterfly pupae, however with some species the rings are so tightly packed that it is not possible to be certain of their sex.
Wherever possible I have included examples of male and female pupae with the life cycles of the species illustrated on this website. When time permits I will add examples to this page from the main Lepidoptera families to illustrate the considerable range of differences between families and in some cases within family groupings.
The S4 segment on female Hawkmoth pupae vary considerably as shown by the following examples:-
The Silver-striped Hawkmoth
I have just been sent examples of empty male and female pupal cases of this species (i.e. after the adults have emerged). The image below shows a comparison between the S4 and S5 segments of the two sexes. The side of the female S4 segment nearest to the cremaster only has a small 'U' shaped curvature in the centre and in this case the female slot is in two parts which are clearly visible - one in each segment.
The Death's-head Hawkmoth
Examples of female and male pupae of this species are shown below. With this species the cremaster side of the S4 segment has a significant curvature towards the female slot.
The Square-spot Rustic
Examples of female and male pupae of this species are shown below - these pupae are a bit 'crinkly'! The division between the female S4 and S5 segments is not so clear in this example.
The Shaded Pug
Many of these species are somewhat harder to sex, particularly the smaller pupae such as the Pugs. Examples of female and male Shaded Pug pupae are shown below. The kidney shape around the male slot is one of the most distinctive features with these smaller pupae. You need a good magnifying glass of at least x10 to sex these pupae but it is much easier with a x20 microscope.
The Canary-shouldered Thorn
Examples of female and male Canary-shouldered Thorn pupae are shown below. The female slot is not so well defined and extends over S4 and partly over S5, the male has the distinctive kidney shape on S5 which is a good distinguishing feature. These pupae are over twice the size of the Shaded Pug.
It is possible to sex the pupae of some butterfly species using the same pointers as for moths. How easy it is depends on the shape of the pupa and whether the pupal segments are flexible, for example the Green Hairstreak butterfly pupae illustrated below have quite small segments and are not very flexible. With this species it is difficult to distinguish the S5 segment on the male pupa so the most positive identification of the sex of these pupae is probably the presence or absence of a slot on the S4 segment.
The Green Hairstreak
The Small White
It is relatively easy to sex the pupae of the Small White as shown in the example below.
Thanks to Angie Seymour for sending me the Silver-striped Hawkmoth pupal cases.
© Reg Fry January 2014