Immature Stages of Mantispidae
The eggs of Mantispidae are stalked like those of Chrysopidae and are laid in autumn in clusters on tree bark, etc., seemingly without relation to the host. Hatching occurs ca. 3 weeks later, and young larvae hibernate without feeding. The following spring or early summer, when the spider egg masses have been laid, they search them out, tearing a hole in the covering to enter. They then wait until the spider eggs hatch, after which they feed rapidly and extensively. There is a molt immediately after hatching, and a second one (the last) after some feeding. The 3rd instar scarabaeiform larvae differ from the active campodeiform 2nd instar (see Clausen 1940 for diagram).. Its head is small; abdomen very large and the legs are rudimentary. it is not able to move in an orderly fashion. The larva completes feeding and spins its yellow oblong cocoon in which the pupa is formed within the unbroken larval skin. After a while the pupa forces its way out of the old larval skin, cocoon, and the host egg sac, wanders about for a while and eventually casts its skin to release the adult.
Observations were made on several species of Mantispa by Smith (1934). One female of M. sayi Banks laid 2,200 eggs, in 6 batches, during ca. one month. These were placed in dense clusters and hatched in 9-11 days. The young larvae were very active but could not be forced to enter spider egg sacs or to feed on eggs, and all died in a short time. The females of M. brunnea Say were found hiding in flowers, in this position they were able to capture readily other insects that visited the flowers. These females were similar in form and color to Polistes. When confined in cages, they lived ca. 1 month and laid ca. 250 eggs each. The eggs are elongated oval and salmon or cream colored. They are borne on slender stalks ca. 1.5X as long as the egg itself.
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A single female of Climaciella brunnea var. occidentalis Banks was found to lay 1,028 eggs in a single cluster in one day (Hoffman 1936). They were salmon-colored and each stood on an exceedingly slender stalk which was lightly longer than the body of the egg. The incubation period took 28 days. Young larvae were able to stand erect by the use of their caudal sucker. Some of these larvae were kept alive for 4/5 months without food, suggesting an overwintering habit similar to Mantispa.
Kishida (1929) found as many as 8 larvae of Eumantispa harmandi Nav. in cocoons of several spiders in Japan. One of these spiders forms its egg sacs in curled leaves of various grasses, while another burrows in the soil. There were two larval instars, and the last was similar to that described for M. styriaca.
Brauer (1869b) recorded Symphrasis varia Er. as parasitic in the nests of a wasp in South America, the cocoon being spun in the cell. Clausen (1940) was not certain that this observation was accurate, however.