A New(ish) Cat and the Joy of Shieldbugs

Dear Readers, this magnificent black cat has been visiting the garden ever since lockdown started. He wanders down the side entrance, and I can always tell that he’s coming because the blue tits and the robins start their chorus of chinking and tsicking. He gets to the corner and has a quick look to see if anyone is there. If I’m having my coffee, he proceeds a little more carefully .  If I think he’s looking too predatory I will stand up abruptly and that’s enough to send him elsewhere for half an hour. If he looks relaxed, I’ll watch him as he strolls around ‘his’ domain and plonks himself down in the sun.

Photo through the kitchen window (not cleaned since lockdown, sorry!)

I love cats, and yet at certain times of the year I will discourage them from the garden whenever I see one (apart from Bailey of course. I think a bird could land on his back and he’d pay no attention). When the new fledglings first appear, I am hypervigilant. If there’s been a particularly cold snap and the birds are too hungry to take their usual care I will be keeping an eye open for hidden felines (though it’s much harder for them to hide when there isn’t so much foliage). I love cats, but I have no illusions about the damage they do.

I do think that prey animals know whether a cat is in hunting mode or not, though. My Mum’s enormous fat old cat, Snuggles, could lay on the patio surrounded by sparrows and they would ignore him. When I was in India I noticed that a tiger in plain view was not seen as a problem while everyone could see it and keep their distance. There sometimes seems to be an uneasy truce between predator and prey, a fine balance that it only takes a twitch of the tail or a tightening of concentration to disturb. There are so many dramas played out every day in an average garden, and lockdown has given me the chance to tune in to some of them.

What a beautiful, beautiful cat though. It is a pleasure to watch him.

And now, for something completely different. I was asked to identify some insects earlier this week by Mrs K over at Old Yarns and Woolly Thoughts She had found some unusual creatures under one of her strawberry leaves and wondered what they were.

First instar Green Shieldbugs (Palomena prasina) (Thanks to Mrs K for the photo)

I recognised them as shieldbugs, and with the help of the Insects and Other Invertebrates of Britain and Europe Facebook group we were able to identify the species – green shieldbug (Palomena prasina). I had one of these in my kitchen a few years ago – when they grow up they are very fine critters indeed.

Shieldbugs are ‘true’ bugs (I know in the US all insects are often known as bugs). A true bug feeds on the juices of plants or animals, and has specially adapted mouthparts to enable it to puncture its ‘victim’. It’s a varied family, with aphids and bedbugs being the villains of the piece, while pond skaters and water boatmen are all over the pond during the summer. I have written about froghoppers and their cuckoo-spit several times, but had no idea that we have a cicada species that lives in the New Forest.

Shieldbugs are named for the shape of their carapaces, but also have the less flattering name of ‘stinkbug’ – if handled they can produce a noisome chemical that is described, in Bugs Britannica by Peter Marren and Richard Mabey, as smelling like ‘rancid marzipan or mouldy almonds’. As anyone who watches Miss Marple or Hercule Poirot knows, the smell of bitter almonds is never a good sign, as it usually indicates cyanide. These bugs are probably poisonous little mouthfuls,

The green shieldbug, like all shieldbugs, goes through a wide variety of forms before it reaches adulthood – each one is known as an ‘instar’, and the shieldbug moults up to half a dozen times after it hatches. The mother green shieldbug lays three or four batches of eggs, each in a hexagonal shape, as you can see from Mrs K’s photograph above. Once the youngsters hatch, they stick together for protection – they produce what’s known as an aggregation pheromone, a chemical which encourages them to stay close. However, if danger does appear they instantly produce a dispersion pheromone, which causes them to run away from one another.

Photo One from https://www.britishbugs.org.uk/heteroptera/idcards/life_stages.html

The different instars of the green shieldbug (Photo One)

The green shieldbug does feed on blackberries, raspberries and green beans, but the insects are rarely found in large numbers, and, to my mind at least, are best admired and left alone. There is a new kid on the block, the southern green shieldbug (Nezara viridula), who turned up in Kings Cross in London at Camley Street Nature Reserve in 2003, and there are some concerns that this little chap might be more voracious than the native species. So far the species hasn’t been spotted further north than Barnet, but it’s probably worth keeping an eye open for.

Photo Two by Rison Thumboor from Thrissur, India / CC BY (https://creativecommons.org/licenses/by/2.0)

Southern green shieldbug nymphs (Photo Two)

The adult southern green shieldbug has clear wings, as compared with the green shieldbug (in my photo of the insect on my kitchen worktop above, you can see that it has amber-coloured wings), but it also has three white spots on the thorax which are pretty much diagnostic.

Photo Three by Katya from Moscow, Russia / CC BY-SA (https://creativecommons.org/licenses/by-sa/2.0)

Adult southern green shieldbug (Nezara viridula) (Photo Three)

I can’t leave the subject of shieldbugs without mentioning the parent bug (Elasmucha grisea). While most insects lay their eggs and do a runner, the female parent bug crouches over her brood of eggs for two to three weeks – the number of eggs laid seems to depend on the body -size of the female. She protects them by making threatening movements towards any interlopers and, if all else fails, she will produce the almondy defensive chemicals mentioned above.

When the eggs hatch, the nymphs stay close together and feed on their eggshells – if one of them strays, the female reaches out with her antenna and guides them back to the shelter of her body. Once they start moving around to feed, the female stays in close attendance, keeping them together. The youngsters hatch asynchronously, and as the larger nymphs move away from the female they join up with others to form mixed groups – it’s been shown that these groups have a much better survival rate than individuals.

Finally, and most amazingly, adult females will sometimes join up and jointly guard all of their eggs and nymphs, with no favour shown to their own youngsters. Pairs of females seem to have the highest nymph survival rate of all. Teamwork in bugs! Who knew. Every single day I am astonished by what I discover for this blog.

Photo Four by By Bj.schoenmakers - Own work, CC0, https://commons.wikimedia.org/w/index.php?curid=40664722

Parent bugs (Elasmucha grisea) joint guarding eggs (Photo Four)

Photo Five by By Aiwok - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=15551532

Single parent bug guarding eggs (Photo Five)

Well, I don’t know about you but shieldbugs have really gotten my attention now. I’m not the first person either: in Bugs Britannica, Peter Marren describes a book called ‘The Shieldbugs of Surrey‘, which gives helpful tips on keeping shieldbugs in captivity (not that I’m advocating such a thing of course). I find this utterly charming, probably because it’s just the kind of thing that I might have written when I was bug-smitten as a youngster.

‘If a fat bug refuses to eat, then it is probably close to a moult. If a thin bug does not eat, then there’s something wrong with the food….if a bug is running around wildly, then it may be in need of a drink….Sometimes a bug may be found lying on its back and waving its legs in the air. This is nothing to worry about….the creature may just be stuck’.

Photo Six by Line Sabroe from Denmark / CC BY (https://creativecommons.org/licenses/by/2.0)

Green shieldbug eggs just before hatching. Look at all the little faces! (Photo Six)

Photo Credits

Photo One from https://www.britishbugs.org.uk/heteroptera/idcards/life_stages.html

Photo Two by Rison Thumboor from Thrissur, India / CC BY (https://creativecommons.org/licenses/by/2.0)

Photo Three by Katya from Moscow, Russia / CC BY-SA (https://creativecommons.org/licenses/by-sa/2.0)

Photo Four by By Bj.schoenmakers – Own work, CC0, https://commons.wikimedia.org/w/index.php?curid=40664722

Photo Five by By Aiwok – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=15551532

Photo Six by Line Sabroe from Denmark / CC BY (https://creativecommons.org/licenses/by/2.0)

9 thoughts on “A New(ish) Cat and the Joy of Shieldbugs

  1. Anne

    Another delight: I too enjoy the company of cats. Our last cat used to ‘bird watch’ with me. No matter where she was in the garden – or how hot it was – once she spotted me sitting down with a notebook and a cup of tea, she would plonk herself on my lap. The birds ignored her presence. Shield-bugs – or stinkbugs – are fairly common here too. I can attest to the dreadful smell if one accidentally crushes one underfoot or flicks it away too hard.

    Reply
    1. Bug Woman

      It does mention in one of my insect books that the stinkbugs in Europe are not as stinky as the ones in tropical countries. Sounds like you should never mess with a stinkbug!

      Reply
  2. Mrs K

    Really enjoyed reading this and am glad that I was a teeny bit of inspiration for it 🙂
    I’ve been looking under other leaves in my garden in case there are any more shield bug babies (photo six is just so gorgeous) but haven’t had any luck so far. I feel guilty about having thrown out the ones I found, but at least they went into the green bin. Thanks for a very interesting and informative read.

    Reply
  3. Bobbie Jean

    Thanks for identifying the Southern green shield bug nymphs for me. I’ve noticed them on my fig tree. It’s adept at eluding the camera lens so I haven’t been able to get a single shot so far. I asked Google if they damage fig leaves. They do. Biodegradable soap is recommended as a deterrent but I wonder what it does to the fruit and leaves.

    Reply
    1. Bug Woman

      Hi Bobbie Jean! I think a lot depends on the size of the infestation – a few shieldbugs won’t do a lot of harm, but obviously hundreds will. I sometimes find that a straightforward hosing down of a plant is enough to deter some bugs…

      Reply

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