5E: Monstrous Arthropods for Fifth Edition

[Cleon]

Decided to go for:

Giant Damselfly 6 feet long, 6 to 8 foot wingspan, weight 50 pounds;
 Variant: Small Giant Dragonfly 4 to 4½ foot long, 7 foot wingspan.
Giant Dragonfly 7 to 8 feet long, 10 to 12 foot wingspan, weight 250 pounds;
 Variant: Big Giant Damselfly 10 foot long, 10 to 14 foot wingspan.
Imperial Giant Dragonfly 12 feet long, 20 foot wingspan, weight 1,000 pounds;
 Variant: Imperial Giant Damselfly 15 to 18 feet long, 18 to 25 foot wingspan.
Tropical Giant Damselfly 30 feet long, 30 to 45 foot wingspan, weight 4,000 pounds;
 Variant: Tropical Giant Dragonfly 16 to 20 feet long, 32 to 36 foot wingspan.

Have updated the Working Drafts appropriately.

If I do decide to add the supersize dragonfly, it'd be:

Tropical Gigantic Dragonfly 20 to 24 feet long, 40 foot wingspan, weight 6,000 pounds; Tropical Gigantic Damselfly 40 feet long, 40 to 60 foot wingspan.

Also, I've been wondering about adding Tiny examples (a) just out of completeness, and (b) to represent the largest of the prehistoric Griffinflies (Meganisoptera) like Meganeura and Meganeuropsis, and (c) to have stats for Tiny giant odonatid nymphs.

Those would be:

Meganeurid (Tiny beast) 15–20 inches long, 20–30 inch wingspan, weight 12 to 24 ounces.

That's extremely large for a meganeurid and way heavier than they actually were. An engineering model puts their mass at around 100 to 150 grams, or between a third and a quarter of a pound.

That isn't a concern, since obviously the D&D Multiverse's physics are different than on Earth, since creatures the size and weight of whales can fly!

 

[Cleon]

I'd copy-and-pasted some of the lengths and weighs into the wrong Odonatids and had to edit the previous post.

Speaking of which.

That's extremely large for a meganeurid and way heavier than they actually were. An engineering model puts their mass at around 100 to 150 grams, or between a third and a quarter of a pound.

Glanced through that paper and it includes some figures for bodyweight of regular dragonflies.

That's very handy, since I can use them to fact check whether my weights are OK.

If I calculate what these Odonates would weigh if I scaled them up to a metre long I can compare the weights of the resulting "Metre Bulk Index" (MBI). A term I just make up inspired by the BMI (Body Mass Index) used to guess whether humans are too fat or thin.

Species​	Dragonfly​	Length (mm)​	Mass (g)​	MBI​
Epitheca cynosura	Common Baskettail	20	0.175	21.875 kg
Micrathyria atra	Black Tropical Dasher	20.5	0.214	24.840 kg
Anax junius	Green Darner	40	0.804	12.562 kg
Anax junius	Green Darner	40	1.038	16.219 kg
Macromia taeniolata	Royal River Cruiser	55	1.18	7.0924 kg
Petalura ingentissima	Giant Petaltail	70	2.0	5.8309 kg
Namurotypus	Namurotypus (Extinct)	165	18	4.0070 kg
Meganeura monyi	Meganeura (Extinct)	350	138	3.2187 kg
Odonate (4 ft., 50 lb.)	Small Giant Dragonfly	1,220	22,700	12.50 kg
Odonate (4½ ft., 50 lb.)	Small Giant Dragonfly	1,372.25	22,700	8.78 kg
Odonate (6 ft., 50 lb.)	Giant Damselfly	1,830	22,700	3.79 kg
Odonate (30 ft., 4k lb.)	Tropical Giant Damselfly	9,150	1,816,000	2.37 kg

So the Small Dragonfly is roughly similar in build to an Green Darner (Anax junius) or Royal River Cruiser (Macromia taeniolata) dragonfly but is built about half as heavy as the bulkiest species, the Black Dasher (Micrathyria atra) and Common Baskettail (Epitheca cynosura).

Meanwhile, the Giant Damselfly and Tropical Giant Damselfly are both lighter than the lightest dragonfly in the table, the Giant Petaltail (Petalura ingentissima, The former is 65% as heavy, while the latter is 40.6% as heavy. Considering how skinny helicopter damselflies are compared to dragonflies, that seems reasonable. If scaled evenly, that'd make the tropical damselfly is 63.75% narrower in build than the Petaltail, which feels about right.

Interestingly, the Giant Damselfly is very close to the paper's estimates for Meganeura monyi.

I could maybe modify the weights to be a bit higher or have a range of weights in order to match the table better, but the current values seem in the right ballpark and it'd have to be quite a wide range since the heaviest dragonfly is 4.2 times sturdier built than the lightest, implying that it's a bit over twice as thick.

If the Small Dragonfly weighed, say 50 to 80 pounds then a metre-long specimen of the same build would weigh between 20 kg and 8.78 kg while a Giant Damselfly with the same range would be 3.79 to 5.9 kg.

Doing the same to the regular Giant Dragonfly would make it 250-400 pounds, the Imperial becomes 1,000 to 1,600 pounds and the Tropical 4,000 to 6,400.

Don't really like those figures though. For a start, 80 pounds seems too heavy for a Small creature unless it's a particularly hefty one.

I think I'll leave the weights as they are, since the dragonflies are within the range of the table.

EDIT: Came across another data point from Wikipedia's List of largest insects which I'll add here for later reference. It's hardly peer-reviewed though.

Might add other entries later if I come across any that are interesting.

Species​	Dragonfly​	Length (mm)​	Mass (g)​	IMBI​
Tetracanthagyna plagiata	Gigantic Riverhawker	120	7	4.0509 kg
T. plagiata (revised)	Gigantic Riverhawker	100	7	7.0000 kg

That seems a bit low.

Most sources I see say Tetracanthagyna plagiata goes up to 100mm not the 120mm Wikipedia said. If I use that body length with the same weight the MBI is very close to the Royal River Cruiser (Macromia_taeniolata), which judging by the similar-looking build seems about right.

It's also within acceptable distance to my Small Giant Dragonfly's MBI, for what that's worth.

 

[Cleon]

Okay, I fancy starting with a Giant Dragonfly conversion but don't feel energetic enough to start number-crunching. Plus it's getting late over here.

I'll just post a blank "Working Draft" as a placeholder.

I've replaced this post with a Want List of Monstrous Arthropods.

 

[Casimir Liber]

Wow...a want list. Been busy but impressed. 5e does lack for invertebrates...

 

[Cleon]

Wow...a want list.

Just remembered you said we "have to do" the BECMI Dragonfly, so I've added those to the Want List.

Wow...a want list. Been busy but impressed. 5e does lack for invertebrates...

Look, I'm only doing Arthropods here, the other spineless wonders will have to wait!

 

[Cleon]

Just remembered you said we "have to do" the BECMI Dragonfly, so I've added those to the Want List.

Renamed them from the original BECMI "Dragonfly" to "Dragon Fly" to further distinguish them from the fully insectile "Odonatid, Giant (Giant Dragonfly)".

Also added five subentries for each colour of Dragon Fly.

Should I create a thread for BECMI conversions to do them in? Assuming we ever get around to them!

EDIT: Did some tweaks to the Odonatid names in the Want List.

 

[Cleon]

Should I create a thread for BECMI conversions to do them in? Assuming we ever get around to them!

EDIT: And the answer is… might as well!

Started a Converting BECMI Monsters to Fifth Edition thread and updated the Completed Fifth Edition Creatures Index to account for it.

Which reminds me, would you mind doing a D&D Beyond version my Grassling conversion so I can update the Indexes?

The Enworld version's done and dusted.

 

[Cleon]

I'm wondering about giving some of the Giant Odonatids proficiency in Perception, since they're said to have the best vision of any insect.

Maybe drop their Wisdom a couple of points to WIS 10 (+0) and give them Skills Perception +2 (the same as a Giant Poisonous Snake, Octopus, or Shark and better than a Frog's +1), with the Tropical Damselfly & Dragonfly having Perception +3 as they have a higher Proficiency Bonus.

That'd give them better eyesight than a Giant Tabanid (WIS 10 and Keen Sight, Perception +0) but not as good as most predatory birds (Eagles and Hawks have Perception +4, Owls and Vultures have +3; all with Keen Sight). or mammals (Dogs, Jackals, Weasels and Wolves have +3; but their Keenness is Hearing & Smell, not Sight).

…and they've shortchanged Cats by giving them either Keen Smell or nothing with their Perception +3. Since when do Felines have noses that smell as well as a Cani but worse hearing? Further evidence for an ailurophobic bias in recent Dungeons & Dragons. Bring back the AD&D Killer Housecat!
​

Hmm, we could leave them with WIS 12 (+1) for Skills Perception +3 as that's what the Giant Wolf Spider has. Lycosids have good eyesight, although not as good as Salticid (Jumping Spiders).

Actually, that raises a point.

I'm statting my Tropical Gigantic Damselfly as a Huge helicopter damselfly, a variety of odonatid that eats giant spiders.

Both the SRD Giant Spiders have Stealth +7, so if the Tropical Damselfly only has passive Perception 11 going for it they'll have a hard time beating that. The damselfly will have a hard time eating any Giant Spiders if it can't find them!

That argues for giving it Perception proficiency, and if Tropical Damsels have it then wouldn't at least some of the other giant odonatids deserve it too?

 

[Cleon]

This is what I've got so far:

Description

Helicopter damselflies include the longest and widest of all Odonata, with even the mundane species growing up to 6 inches in length (The giant helicopter Mecistogaster linearis) or an 8 inch wingspan (The blue-winged helicopter Megaloprepus caerulatus). A mammoth helicopter damselfly is truly enormous, typically 30 feet long, with a 30 to 45 foot wingspan, and weighs about 4,000 pounds or 2 short tons. They dwarf a regular giant dragonfly (see Giant Dragonfly), although some tropical giant dragonflies are heavier and even more powerful (see Titanic Dragonfly).
 These tropical damselflies have extremely elongated and narrow abdomen, and equally slender wings that often have a spot or band of color at the end. A flying helicopter damselfly resembles a pinwheel fluttering and swirling in midair, or a hovering windmill for a mammoth giant helicopter. Their wings appear to spin around the thorax, as if the insect was corkscrewing itself through the air, an illusion that lead to the common name of helicopter damselfly.
 Helicopter damselflies live in rain forests and jungles. The normal version can be fairly common, but mammoth helicopter damselflies are extraordinarily rare due to the unusual habitats they need. This rarity has led to many legends, rumors and tall tales, a few of which might contain a few grains of truth. These stories include:

• Mammoth helicopter damselflies were created by a forgotten insect-headed god to protect its temples and worshippers. The civilization is long dead, with its cities lost in the heart of a colossal jungle, but the mammoth damselflies still faithfully patrol its ruins.
• These great insects are solitary queens, each served by a hive of lesser giant damselflies (e.g. the Giant Damselfly or Giant Tropical Damselfly), while larger ones (e.g. the Imperial Giant Damselfly) guard the queen's boudoir and the hive's treasures.
• A mammoth helicopter damselfly is an artificial species invented by a mighty wizard, solely to annoy drow elves by eating the giant spiders that drow love.

 Jungle Dwellers. A mammoth helicopter damselfly is an extremely precise and agile flier, but is so gigantic it still needs around 50 feet to fly through a gap. Therefore any rainforest it navigates must have the majority of its trunks spaced at least that far apart. Their preferred habitat are spectacular jungles of mysterious and possibly magical origin that have other giant arthropods as their primary fauna. While they could adapt to other hot and humid places with suitable prey and breeding pools, the only non-rainforest habitat they're known to favor are ruined or abandoned cities with buildings tall enough to fly between. Tropical gigantic damselflies will venture into the open on short hunting expeditions or seek a new territory after being driven away by rivals, but in an open environment they are out-competed by other flying predators, particularly gigantic tropical dragonflies and kaleidoscopes of imperial giant tropical dragonflies (see Titanic Tropical Dragonfly and Imperial Giant Dragonfly, or the Mammoth Tropical Dragonfly below).
 Wings in the Dark. Many tropical odonatids like to perch in the shade of vegetation, both to hide from predators and to avoid overheating from the warmth of the sun. Helicopter damselflies, living as they do beneath the forest canopy, spend most of their lives in the shadows. When they do venture out of the cover of the trees, helicopter damselflies prefer gloomy overcast conditions over hot and sunny days. Normal-sized helicopter damselflies hunt and breed during the day then rest at night, as is usual for odonatids, but the monster variety has gained both blindsight and darkvision, allowing giant helicopter damsels to hunt at night as easily as day. A giant helicopter damselfly may be nocturnal (active at night) and/or crepuscular (most active at dusk or dawn), or hunts whenever it is hungry regardless of the time, but avoids going out in bright daylight when it doesn't have to.
 Spider Hunters. Normal helicopter damselflies specialize in hunting spiders. They slowly fly up to webs and pluck off the spider or the spider's silk-wrapped prey, which are devoured in midair. A monstrous helicopter damselfly still likes to attack spider webs, but is also a generalist hunter who will snatch prey from the ground, air, and trees. Like a regular damselfly, it only catches prey it can carry through the air. That is no great restriction, as a mammoth helicopter damselfly can lift 1,200 pounds while flying, enough to carry creatures as heavy as giant spiders, average-sized brown bears and riding horses, or giant horseflies (see Giant Tabanid). Giant helicopter damselflies prefer non-flying prey and rarely engage in aerial pursuits like a giant dragonfly or giant tropical damselfly.
 Water Pit Breeders. Natural helicopter damselflies breed in phytotelmata—the pockets of water that collect in vegetation (e.g. holes in trees, hollow tree stumps, broken bamboo, cup-shaped plants like bromeliads, fallen leaves and rinds). Males compete for the best breeding spots and guard the phytotelmata, mating with females before they lay their eggs. While normal helicopter damsels might have difficulty finding a phytotelma, it is almost impossible for mammoth helicopters, since only implausibly colossal plants could hold enough water. Giant helicopter damselflies only breed in still water, so rivers and streams are not an option. Instead, the giant helicopter damselflies usually breed in water-filled pits, such as sinkholes and caves, including artificial ones like cisterns and water tanks. A mammoth helicopter damselfly breeding site will, on average, produce a single adult for every 27,000 cubic feet of water. An Olympic-sized swimming pool (~88,000 cubic feet), for example, would produce around three adults, although as little as 12,000 cubic feet might be enough for a single naiad to reach full size (see Mammoth Damselfly Naiad for statistics).
 The tremendous rarity of suitable breeding sites is the primary restriction on mammoth helicopter damselfly numbers in the jungle. Some mammoth odonatids have nymphs and naiads with adaptations to reduce the limitations of breeding in water (see Giant Dragonfly Nymph for details).

VARIANT: MAMMOTH TROPICAL DAMSELFLY (DIURNAL)
Mammoth tropical damselflies have the same statistics as mammoth helicopter damselflies, except they do not have blindsight or darkvision. They hunt in daylight like their smaller brethren and either have similar proportions to a mammoth helicopter damselfly, or are somewhat shorter: 24 to 30 feet long, 30 to 36 foot wingspan. Some are technically enormous tropical helicopter damselflies that lack the nocturnal adaptations of the standard "Mammoth Helicopter" described above.

VARIANT: MAMMOTH TROPICAL DRAGONFLY
Some varieties of giant dragonfly exceed even the imperial giant dragonfly in stature. A Huge giant dragonfly is approximately 18 to 20 feet long, with a wingspan of 30 to 33 feet. It uses a mammoth tropical damselfly's statistics except for being faster (fly 80 ft., Dashing Flight 80 ft., Dodging Flight 40 ft.) and having no blindsight or darkvision. A mammoth tropical dragonfly nymph grows into as huge and deadly a predator as a mammoth damselfly naiad.
​

Haven't finished yet.

Keep on coming up with ideas for cool varieties.*

* Naturally, by "cool varieties" I'm using the DM definition of "kills PCs in interesting ways!"

 

[Casimir Liber]

That argues for giving it Perception proficiency, and if Tropical Damsels have it then wouldn't at least some of the other giant odonatids deserve it too?

They've all got such huge multifaceted eyes....so yes, I reckon perception proficiency is a must!

Re cool varieties - am keen on the BECMI chromatic "dragon" flies -espeically as I have Tiamat as a villain warping critters!