Protection, Cannibalism and Self-Sacrifice: The World of Spider Parenting

When someone mentions parental care in the animal kingdom, birds and mammals are probably the organisms than spring to most people’s minds, and it’s most likely that invertebrates and specifically spiders are not high on peoples lists of the animal kingdoms most devoted parents. It is true, the invertebrate world is neglecting in parental care examples, with the offspring normally having to fend for themselves immediately after hatching. However, even though the majority of hatchling invertebrates are left to their own devices, there are a number of groups and species that do display varying degrees of parental care and, this is no less true for the spiders.

Firstly, spider eggs are not laid out in the open, or buried, but the females make use of their silken abilities and contain the eggs within a silk pouch, known as an egg sac. These are then, more often than not, defended from predators by the females and then once the young hatch they leave their mothers web and venture out on their own. Some spiders take this protection a step further; for example, wolf spiders – species belonging to the family Lycosidae – are active hunters and do not reside in a web. Females therefore carry their egg sacs on the back of their abdomen and even alter their activity

Nursery web spider
Female nursery web spider (Pisaura mirabilis) guarding her nursery of spiderlings

patterns in order to ‘sun’ the eggs and maintain an optimal temperature (Bonte et al., 2007). Furthermore, once the young have hatched they are carried on the mothers back and the females have even been observed to help the offspring drink by sitting in water. Lycosids are not the only spiders that carry their egg sacs and extend protection after hatching; nursery web spiders (family Pisauridae) also demonstrate this kind of parental care. The female nursery web spider will carry her egg sac using her chelicerae and once they are ready to hatch will spin a silken ‘nursery’ in which the offspring can reside in until they are ready to face the world on their own. Recently, maternal care has even been found in pirate spiders (family Mimetidae) which is surprising considering their araneophagic (they eat other spiders) lifestyle (Benavides et al., 2017).

Whilst it is well known that female spiders often provide their young with some degree of protection, it wasn’t until recently that evidence for parental care in spiders was

paternal spider
Male Manogea porracea (Moura et al., 2017)

found. A study by Moura et al. (2017) observed male Manogea porracea providing their young with protection. The study found that male M. porracea provide a number of parental services, first of all they actively protect the offspring from two araneophagic (spider-eating) spiders, Faiditus caudatus and Argyrodes elevates. Secondly, the male spiders were seen to aid in the maintenance of web integrity and structure, as well as ensuring the safety of the egg sac. This type of active parental care has never been observed in a solitary spider species before and thus, is really quite fascinating. They found no increase in offspring survival due to the added protection of the male, however towards the end of the reproduction cycle when females have deserted the young or died the male continues to provide care: a very interesting case of changes in sex-specific care behaviours, previously unseen in spiders (Moura et al., 2017).

paternal spider
The position on the web the male M. porracea takes up in the absence of the female (Moura et al., 2017)

There are spiders that take the devotion to their offspring’s a step further, in the form of matriphagy. The reproduction cycles of numerous spider species involve matriphagy, which is the ritual of the offspring consuming their mother. Studies of matriphagy on a variety of spiders have shown the process to have a number of benefits for the survival of the young. For example, Kim et al. (2000) found that in the lace web spider (Amaurobius ferox) the consumption of the mother greatly affects the offspring’s development and mortality rates. It was shown that the spiderlings experienced a two or three-fold body mass increase on the day off the matriphagy which then sets them up for long term survival. Young that were deprived of the chance to consume their mothers suffered a delay in the timing of their third moult and an increase in mortality; this is thought to be due to the abnormal moulting and less effective prey subduing due to a lack of food (Kim et al. 2000). Now, you may be wondering why a female would sacrifice herself, yes it benefits her young, but it also prevents her from reproducing multiple times which would also increase the chances of her genetic information surviving. However,whilst female A. ferox spiders that are prevented from being consumed by their children do produce a second egg sac, the clutch is around half the size of the first (Kim et al., 2000) and with spiderlings mortality rates being generally high, it may be more effective for the female to completely devote and sacrifice herself for one brood. Matriphagy is observed in numerous spider species, including Stegodyphus lineatus, the female of this species will feed her young through regurgitation and then is consumed as a final meal before the spiderlings disperse (Salomon et al., 2005).

Further, the parental care of spiders does not stop there and once again it is not only the females providing it. Male spiders will also give their lives to ensure their young have the best chance of survival possible, this time in the form of sexual cannibalism. Females consuming their partners is well documented in the invertebrate world with praying mantis and widow spiders being the common examples, however, it occurs in a huge number of spider species and has a number of benefits for the offspring. Welke and Schneider (2012) found that female wasp spiders (Argiope bruennichi) that consumed

11894463_10153533877617224_2694742867966769089_o
Female Argiope bruennichi guarding a large egg sac (photo credit: Josh Phangurha)

their male partner had a greater fecundity and produced offspring with an increased ability to survive starvation under winter conditions. This could prove to be particularly beneficial to the more northern populations of this species where extended winters and cold snaps could delay development, therefore giving the offspring of cannibalistic females an advantage (Welke and Schneider, 2012). Now, some may say that the males are not providing the care here as the females will likely eat them regardless of their desire. This may well be true for A. bruennichi; however, it looks as though male redback spiders (Latrodectus hasselti) offer themselves willingly for female consumption by positioning themselves above the female’s jaws (Andrade, 1996). This, again appears to have a couple of advantages for the male, firstly males who are consumed mate for longer and fertilise a greater number of eggs than males that survive (Andrade, 1996). Furthermore, females who consume their first mate were more likely to reject further courtship opportunities, therefore increasing the chance of single paternity (Andrade, 1996). So, it would seem there are benefits to allowing your mate to devour you.

Right! Well there we have it, spiders are more dedicated and devoted parents than we all thought. Not only do they provide their young with protection, they go far beyond that and give the ultimate sacrifice by allowing either their children or their mate to consume them. Of course, it isn’t all that selfless considering the fact that it is in their best interests to see that their offspring survive to reproduce. Spiders display a fascinating array of parental care methods with new examples still being discovered. Paternal (and other methods of parental) care may be more common than we think, just yet to be observed. So, the next time the topic of parental care comes up at a dinner table (because when does it not) or a pub quiz, don’t forget to think of the devoted, self-sacrificing spiders!

Thanks for reading this longer and different styled post to what I normally write. I hope you have enjoyed it as much as I enjoyed writing it. I’m planning on doing a mix of both light reads (like my previous posts) about what I’ve been up to and my photography etc. As well as some more in-depth posts like this one. Feel free to comment or contact me with feedback (positive or negative) on either style, always looking to improve my content. Again, thanks for reading!

Follow me on twitter: Matthew Woodard @ZoologyNotes

Photo credit: Josh Phangurha (female wasp spider). Check out his instagram for awesome wildlife pictures accompanied by fascinating insights into the subject biology.

References

Andrade, M.C.B. (1996). Sexual selection for male sacrifice in the Australian redback spider. Science, 271(5245), 70-2.

Benavides, L.R., Giribet, G. and Hormiga, G. (2017). Molecular phylogenetic analysis of “pirate spiders” (Araneae, Mimetidae) with the description of a new African genus and the first report of maternal care in the family. Cladistics, 33(4), 375-405.

Bonte, D., Belle, V.S. and Maelfait, J.P. (2007). Maternal care and reproductive state-dependent mobility determine natal dispersal in a wolf spider. Animal Behaviour, 74(1), 63-9.

Kim, K.W., Roland, C. and Horel, A. (2000). Functional value of matriphagy in the spider Amaurobius ferox. Ethology, 106, 729-42.

Salomon, M., Schneider, J. and Lubin, Y. (2005). Maternal investment in a spider with suicidal maternal care, Stegodyphus lineatus (Araneae, Eresidae). OIKOS, 109, 614-22.

Moura, R.R., Vasconcellos-Neto, J. and Gonzaga, M.O. (2017). Extended male care in Manogea porracea (Araneae: Araneidae): the exceptional case of a spider with amphisexual care. Animal Behaviour, 123, 1-9.

Welke, K.W. and Schneider, J.M. (2012). Sexual cannibalism benefits offspring survival. Animal Behaviour, 83, 201-7.

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